To provide a method of manufacturing a molded product which can be suitably used for manufacturing in a simple way without the reduction of the quality of the product.

In the manufacturing method of a case 100, a molded product which, on a case body 10 which is an intermediate product consisting of a resin material and forming a first molding part, has a grip 20 consisting of a material different from the material of the first molding part and making a second molding part and a waterproof cover 30 joined by integral molding, the method comprises a step of providing a coat on the surface of the case body 10 of the intermediate product and a step of arranging the coated case body 10 in a mold and integrating by molding the grip 20 of the second molding part and the waterproof cover 30 with the case body 10.