A blow molding device, having: a mold; a blow nozzle tightly communicating with a mouth tubular part of a preform when the preform fitted in the mold; and a stretch rod, the blow molding device imparting shape to a container by longitudinally stretching the preform by means of the stretch rod and stretching the preform into an expanded shape by means of a pressurized liquid fed, via the blow nozzle, from a pressurized liquid feeding part separately provided, in which the blow nozzle has a support part for supporting the posture of the stretch rod, and a filling head part communicating with the mouth tubular part of the preform, the filling head part having a feed channel formed therein in the axial direction; and the support part and the filling head part are configured to be detachably coupled to each other in the vertical direction.