A blow molding device includes a blow molding mold to which a preform is fitted, a blow nozzle that is fitted to a mouth tubular portion of the preform, and a pressurized liquid supply unit configured to supply a pressurized liquid to the blow nozzle, the preform being to be molded into a shape conforming to a cavity of the mold by filling the liquid into the preform through the blow nozzle. The blow nozzle includes a central hole and a plurality of peripheral holes having an inner diameter smaller than an inner diameter of the central hole and arranged to surround the central hole. The liquid is filled into the preform through the central hole and the plurality of peripheral holes.