Intake system and method for producing the same

An intermediate resin molded body 30 is put between two outer resin molded bodies 10, 20, and a molten resin is injected substantially simultaneously into a first interface between one outer resin molded body 10 of the two outer resin molded bodies and the intermediate resin molded body 30 and a second interface between the other outer resin molded body 20 and the intermediate resin body 30, so that the two outer resin molded bodies 10, 20 and the intermediate resin molded body 30 are welded together.