A method relates to manufacturing an in-mold decorative molded product including a transfer layer formed on a surface of an injection-molded product. The method includes 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 molding resin into the molding injection space and a structure for holding the in-mold decorative molded product; and forming the in-mold decorative molded product by filling the molding injection space with the molding resin and then opening the first and second molds. When the base film is separated from the in-mold decorative molded product by opening the first and second molds, a peeling weight varies depending on a portion in an end part of the in-mold decorative molded product.