A method of manufacturing an in-mold decorative molded product including a transfer layer formed on a surface of an injection-molded product, the method including: inserting in a first mold for injection molding an in-mold transfer film including the transfer layer disposed on a base film; forming a molding injection space by mold clamping of the first mold and a second mold including a structure for injecting a resin into the molding injection space and a structure for holding a molded product; and forming a molded product by filling the molding injection space with a molding resin and then opening the second mold and the first mold, wherein when the base film is separated from the in-mold decorative molded product integrated with and the transfer layer by opening the molds, a peeling weight varies depending on a portion in an end part of the in-mold decorative molded product so that a peeling starting point is generated from a position with a light peeling weight in the in-mold transfer film to peel the in-mold decorative molded product from the in-mold transfer film.