PURPOSE: To make a space where an extruder occupies small even if the discharge volume is increased, by feeding a molding material that has been heated in a feed hopper to become the molten state into an extruder cylinder under pressure by gas pressure.

CONSTITUTION: The granular molding material 5 is heated in the feed hopper 3 by a heater 6 to be melted so that the molding material 5' is obtained in the molten state. Gas pressure from a pressurized gas supply source 8 is exerted to this molten molding material 5' so that the molding material 5' is fed into the extruder cylinder 1. Since the molding material is melted in the feed hopper 3, the melting function of the extruding cylinder 1 is not required, therefore the grooves in the screw 2 can be deepened, the pitch of the screw 2 can be increased, the conveying ability of the screw itself can be increased, and the volume of the discharge can be increased. Further, when the molding material is fed in the molten state, the amount of inclusion of air can be reduced.