Method for manufacturing foamable injection molding and injection device therefor

An injection apparatus comprising a plasticizing unit that plasticizes a raw material resin and an injection unit that injects a plasticized molten resin, wherein the plasticizing unit is provided with a heating cylinder having a foaming gas injection valve and a screw provided inside the heating cylinder, and

• the rotation and the advance and retreat movements of the screw are controlled such that
• a raw material resin is plasticized by means of the screw inside the heating cylinder of the plasticizing unit and a foaming gas injected from a foaming gas injection valve is dissolved in the plasticized molten resin, and
• after the screw retreats to a prescribed position according as the molten resin accumulates in the front end side of the heating cylinder by the screw that is rotating,
• the screw advances with rotating to cause the molten resin which has been accumulated in the front end side of the heating cylinder to be transferred to the injection unit.