PURPOSE: To improve the safety enabling the prevention of possible ozone and others by introducing ultraviolet rays into a cavity core with an optical fiber from an ultra violet ray source provided separate from the cavity core to irradiate a molding material.

CONSTITUTION: An ultraviolet ray hardening molding material 14 is injected into a die 1 from an injection molding machine 13 to fill the space between a cavity core 5. Then, ultraviolet rays irradiate the cavity 4 and the cavity core 5 separately via an optical fiber 6 from a ultraviolet ray irradiation source 7. The ultraviolet rays are irradiated on the molding material filled between the cavity and cavity core being reflected on reflection layers 8 and 9 to solidify the molding material quickly. The molding thus solidified is released from the die by sticking out an ejector pin 10 from the cavity core 5 at the opening of the die.