To provide a method for manufacturing a resin molded product, which eliminates the terminal processing operation of a second layer when manufacturing a first layer and the second layer by injection molding.

The method for manufacturing the resin molded product includes: a first mold closing process of closing a first mold 40 and a second mold 50, forming such a state that a first core side protrusion part 62 formed on a first core 60 is fit to a first mold side step part 44, thereby forming a substrate molding space 15; a first layer molding process of injecting the resin into the substrate molding space 15 to form a substrate 11; a mold opening process of opening the first mold 40 and the second mold 50; a mold arranging process of arranging the first mold 40 and a third mold 70 oppositely to each other; a second mold closing process of closing the first mold 40 and the third mold 70, thereby forming a body part molding space 25A and causing a second core 80 to come into contact with the first and third molds 40 and 70 to form a folding part molding space 25B; and a second layer molding process of injecting the resin into the body part molding space 25A and the folding part molding space 25B to mold a cover material 21.