This injection molding device has a nozzle (1) for injection molding a biaxial stretch blow molding preform in which at least one intermediate layer is laminated in a base layer. An inner flow channel (15) and an outer flow channel (17) for forming the base layer and a middle flow channel (16) for forming the intermediate layer are disposed coaxially. The middle flow channel (16) is divided into a specified number of flow channels by longitudinal blocking rib pieces (20). The respective upstream portions (20b) of the side walls located on the upstream side of the pairs of side walls (20a) on the two sides of the longitudinal blocking rib pieces (20) in the circumferential direction are inclined surfaces for which the distance therebetween narrows from the downstream side to the upstream side, or the downstream ends of the longitudinal blocking rib pieces (20) enter the inner flow channel (15) and/or the outer flow channel (17).
