PURPOSE: To make the mechanism simple, and to prevent a resin from leaking from an injection nozzle, by allowing a shut-off plate provided to one end of a T-lever to be pressed against or released from a forward tip opening of the injection nozzle.

CONSTITUTION: A cam plate 7 is attached adjacent to a heating cylinder 1 by attaching fitments 8, 8, the forward part and the rearward part of a guide rod 9 are connected via a connecting fitment 10, and the fitment connecting 10 is movably born by the attaching fitments 8, 8. On end of a link 11 is pinned to the connecting fitment 10, and the other end is pinned to a cam roller 13 at 14. The cam roller 13 is engaged with a cam groove 15 of a cam plate 7. The other end of the link 11 is connected to one end of another link 16 via a pin 14, and the other end of the link 16 is pinned to one end of the T-lever 18. The shut-off plate 20 is mounted to the other end of the T-lever. The forward end of a piston rod 22 of a cylinder 21 is connected to the pin 14 of the cam roller 14 to carry out the opening and closing the shut-off plate 20.