This invention relates to a method of producing a molded object made of synthetic resin, and more particularly to an improved method for producing resinous molded articles, especially bottles, having improved and superior surface appearances, less surface imperfections and gloss defects. Conventionally, a variety of methods are known for producing synthetic resin bottles having superior surface appearances, less surface imperfections and gloss defects. A first method is shown in FIGS. 1 to 6 of the drawings. In this method, a blank (FIG. 2) is placed in a female mold (FIG. 1) having a cavity (FIG. 5), a plurality of concave portions (FIG. 3) are formed on the inner surface of the female mold cavity (FIG. 5), and the blank is deformed by pressing the latter against the female mold cavity (FIG. 5), thereby forming a concave part (FIG. 4) in the blank at a position corresponding to each concave portion (FIG. 3). At the same time, a male mold (FIG. 6) having a protrusion is disposed between the female mold (FIG. 1) and the blank in such a manner that a cavity (FIG. 5) defined by the male mold is positioned over the area of the inner surface of the female mold cavity where the concave portion (FIG. 3) is formed. The blank is placed in this state and is then subjected to pressure between the female mold and the male mold to thereby form a protrusion (FIG. 7) corresponding to each concave portion (FIG. 3) and fittingly insert the protrusion (FIG. 7) into the corresponding cavity (FIG. 5). A second method is shown in FIGS. 8 to 11 of the drawings. In this method, an extrusion mold (FIG. 8) is formed in such a manner that the outer peripheral surface thereof has an inner peripheral surface which consists of a concave portion (FIG. 9), an extending portion (FIG. 10) and a protrusion (FIG. 11), wherein a part of the concave portion (FIG. 9) and a part of the extending portion (FIG. 10) correspond to each other, the protrusion (FIG. 11) extends perpendicular to the extending portion (FIG. 10), and the extending portion (FIG. 10) corresponds to the protrusion (FIG. 11). The extrusion mold is formed by use of a conventional molding apparatus. Thus, an intermediate product, which is formed by injection molding (FIG. 7) at a position corresponding to the protrusion (FIG. 11) of the extrusion mold (FIG. 8), is inserted into the extrusion mold (FIG. 8) to the position of the extending portion (FIG. 10). In either method, the protrusion (FIG. 7 or FIG. 11) of the molded object is formed by transferring the protrusion of the female mold or the extruded mold. As a result, the surface of the female mold or the extrusion mold should have a high accuracy. For example, a high-accuracy die must be prepared for forming the female mold or the extrusion mold. A further problem is that the protrusion (FIG. 7 or FIG. 11) formed by the transfer of the protrusion is apt to deform in the case of using a soft material for the blank. As a means for solving the problems noted above, a third method is known wherein the protrusion of the female mold or the extrusion mold is directly transferred to the molded object without using a transfer mold. In such a method, since the surface of the female mold or extrusion mold is in direct contact with the surface of the molded object, it is required that the surface of the female mold or extrusion mold be a mirror surface. Such a mirror surface has such disadvantages that: (1) since the female mold and/or the extrusion mold is required to be polished at the surface thereof, high polishing technique is required; (2) it is difficult to remove burrs and to polish off a burr, and thus the number of processing steps is increased; (3) since it is required to form the surface of the mold having a mirror surface without any projection by means of a relatively simple processing technique, when a molding material having a high quality and superior performance is used, the molding material is likely to be melted due to heat generated in the course of molding, thereby degrading the quality of the molded product and decreasing the dimensional accuracy thereof; and (4) since the polishing accuracy of the surface of the female mold or extrusion mold depends upon that of the polishing device, it is difficult to obtain a stable standard of product quality. Therefore, when the above-mentioned method is employed, it is necessary to employ a material having an inferior performance to meet the requirements of the mirror surface and the mirror surface must be polished by hand. A fourth method is known wherein the protrusion of the female mold or the extrusion mold is directly transferred to the molded object without using a transfer mold. In this method, the protrusion of the female mold or the extrusion mold is formed into a convex shape such that the lower end of the protrusion is higher than its root, thereby allowing the molded object to be held by the protrusion without being fitted therein, as shown in FIG. 13 of the drawings. This method is very advantageous because the structure of the mold is simple and the cost of the molding material is low, but has the disadvantage that, when the molding material having a high quality and superior performance is used, the concave portion having an outwardly curled shape or the other concave portions are formed at the portion of the protrusion corresponding to the root of the protrusion, and thus the outer surface of the molded object has a depressed state. In particular, if an elongated protrusion is employed, a large surface area is depressed. On the other hand, if a small-size protrusion is employed, it is required that the amount of the concave portion formed at the portion of the protrusion corresponding to the root of the protrusion is increased. As a result, the protrusion is very likely to be buckled. A fifth method is known wherein the protrusion of the female mold or the extrusion mold is directly transferred to the molded object without using a transfer mold. In this method, the protrusion of the female mold or the extrusion mold has a cross-sectional shape corresponding to the concave portion, wherein a portion of the protrusion corresponding to the central portion of the protrusion is made smaller than the width of the protrusion (FIGS. 1 and 2), and thus the molded object is engaged by the protrusion without being fitted therein (FIGS. 3 and 4). This method is advantageous in that (1) since a concave portion can be obtained in the blank having a relatively low accuracy, there is no need to use a material having a high accuracy of surface flatness, and the mold has a relatively simple structure, and (2) when the molded object is not fitted in the female mold, the thickness of the molded article can be set to be larger than the width of the protrusion. However, when this method is applied, as shown in FIGS. 1 and 2, since a portion of the protrusion corresponding to the central portion of the protrusion is made smaller than the width of the protrusion, the entire protrusion is pressed into the concave portion of the blank and thus a depression is produced at the central portion of the protrusion. In view of the fact that there are a variety of methods for producing resinous molded objects, and in order to eliminate the above-mentioned disadvantages and to provide resinous molded objects having improved and superior surface appearances, without forming the molded object of a defective shape and without involving manual operations of filling an injection resin in the female