an apparatus for injection molding of plastics material in accordance with a gas or liquid injection method . the apparatus includes a nozzle which can be applied to the injection molding die or the injection mold . this nozzle enables selectively the sole injection of plastics material melt , the simultaneous injection of plastics material melt and medium as well as the sole injection of medium into the mold cavity of the injection molding die or injection mold . the melt is supplied to the nozzle mouth by the extruder screw cylinder of the extruder around a nozzle torpedo , while the medium is introduced into the nozzle so as to be spaced from the nozzle mouth . the automatic operation of the apparatus in the course of all three types of operation is made possible by locating a check valve in the melt supply line of the nozzle between the upstream end of the nozzle torpedo and the junction piece of the extruder screw cylinder , which check valve can be automatically brought into its closed position in direction counter to the extruder screw cylinder .