A system and method for hydraulic blow molding a plastic preform into a container. The system includes a nozzle having a nozzle body with a main bore extending therethrough and an outlet for ejecting molding medium into a preform positioned within a mold. A minimum internal diameter is defined within the body of the preform, which is bound on opposing ends between an open end and a closed end. To form the container, a liquid stream is injected into the preform. The liquid stream is defined by the outlet so as to have an external diameter that is less than the minimum inner diameter of the preform, allowing the stream to impinge upon the close end of the preform without impinging upon a transition of the preform, where the minimum inner diameter of the preform is reduced from the diameter of the finish.

To regulate, in blow molding device using liquid, such as beverage, cosmetic product, and pharmaceutical product, filled in final product as pressurized liquid, head space in container which is filled with content liquid during molding to be predetermined volume, provided is blow molding device including blow nozzle configured to tightly communicate with mouth tubular portion of preform. In state where rod is disposed to be inserted into blow nozzle and where tip portion of rod is inserted into preform, pressurized liquid is supplied into preform via tubular introduction path formed by blow nozzle and rod, thereby expandingly shaping container in accordance with cavity of metal mold. When container is shaped and supply of pressurized liquid is stopped, rod is disinserted from container, and according to shape and insert position of tip portion of rod, head space of shaped container that is filled with liquid is regulated to be predetermined volume.