PURPOSE: To contrive to improve productivity by a method wherein the main body and the lid of a case, both of which are simultaneously molded in an injection mold, are taken out of the mold and the main body and the lid of the case are assembled together during the unloading process.

CONSTITUTION: When the main body 11 and the lid 12 of a case are assembled together in a hand 41, the suction of the suction cups 47 of a suction plate 45, through which an assembled case is held, is released, resulting in placing the assembled case on a belt conveyer 34 by falling. Thus, during the unloading process of the case main body 11 and the lid 12, both of which are molded items, the assembling of the main body 11 and the lid 12 is performed in the hand 41. As a result, the assembling work of the case in the following process is omitted and the productivity of the molded item can be improved.