PURPOSE: To provide the manufacturing method of an urethane-reaction injection molded product, which can stably mold ISF without using fluorocarbon.

CONSTITUTION: A polyol component (b) and an isocyanate component (a) are made to collide and mixed. The urethane-reaction injection molded product of ISF is manufactured with RIM for injecting the mixture into a sealed metal mold 21 by this method. As the molding material, the injection molding material based on the prescription, wherein foaming agent is not compounded, is used. Before the above described collision and mixing, air or inactive gas of 10-30 volume % is blown into the components stored in raw-material tanks 11 and 13.