To heighten the airtightness of this blow molded body by strongly joining a board part with a hollow structural part by a method wherein this blow molded body in despondently consists of the board part and the hollow structural part and both the parts are integrally connected with each other at the hollow end parts of the hollow structural part.
This blow molded body consists of a board part 1 and a hollow structural part 2 so as to integrally connected both the parts with each other through connecting parts 4 at the hollow end parts 3 of the hollow structural part. These parts are made of one end the same thermoplastic resin material. This blow molded body is produced by an injection molding method of an injection pressing method. Its molds consist of molds 12 and 13 having cores 11 for molding the connecting parts 4 and the hollow structural part 2 and, in addition, a molten resin feeding port 9 and a compressed fluid feeding port 10 are provided in the mold 13. The feeding amount of the molten resin is controlled so as to fill some part of a cavity 14 part formed by the cores 11 and the remaining part of the cavity is left un-filled so as to form a gap. After that, compressed gas is fed through the compressed fluid feeding port 10 in the molten resin so as to unload a blow molded body after the cooling of the molded body. Next, the cores 11 are removed from the molded body.