PURPOSE: To simplify a constitution and to prevent occurrence of a switching mark, by forming the second resin path between an inner face of the first nozzle and an outer face of the second nozzle and making the second resin path freely closable by bringing the second nozzle into contact with the first nozzle.

CONSTITUTION: In the neutral state where no injection is carried out, the second nozzle 9 is brought into contact with an inner face of the first nozzle 4 and a valve member 10 closes an injection hole 9a of the second nozzle 9. To inject a skin material under this condition, it is enough to inject a molten resin in the first heating cylinder 1 by forwarding a screw 2 of the first heating cylinder 1. The said resin passes through a passing hole 7 of a cylinder head 3 and a material path 6 and flows into the second resin path 8 and gives a pressure on the second nozzle 9 in the direction separating from the first nozzle 4. On the other hand, the second nozzle 9 is pressed on the first nozzle 4 by means of the valve member 10. Therefore, when the resin pressure of the skin material exceeds the pushing pressure of the valve member 10, the second nozzle 9 is separated from the first nozzle 4 and the skin material is injected from an injecting hole of the first nozzle 4 into a mold.