To provide a method of manufacturing a molded product using an injection molding apparatus in which when carrying out injection molding while expanding and contracting a molding cycle, injection molding can be carried out without generating the temperature difference between a plastic temperature and mold temperature as much as possible at the time of injection in a plastic injection process, and thereby the quality deterioration of a molded product can be inhibited.

The method of manufacturing a molded product using an injection molding apparatus comprises: storing molded products molded by a molding cycle including a low pressure mold clamp process, a high pressure mold clamp process, an injection process which injects plastic measured at a measuring process, and a cooling process which cools the injected plastic in a stocker; and supplying the molded products to a post-process, wherein the molding cycle includes a process which expands or contracts time of the molding cycle, and the process which expands or contracts time of the molding cycle includes: a process which decides delay time according to the stored volume of the molded products in the stocker; and a process which delays the delayed time in the start time of the measuring process of a plastic, and the high pressure mold clamp process start time after the low pressure mold clamp process or the injection process start time after the high pressure mold clamp process.