PURPOSE: To secure the discharging function of the air vents of a metallic mold by a method wherein through holes, a cavity part or a rough surface part are provided in air vent parts so that the resin having entered the air vent parts may adhere to the lead frame side only.

CONSTITUTION: The resin 5 poured from the gate of a metallic mold enters a cavity while discharging the air from the air vents of the metallic mold finally entering the air vents so as to fill up the through holes 3 provided in the air vent parts 2a, 2b, 2c. Next, when the metallic mold is opened after it is filled up with the resin 5 entering the through holes 5,the resin 5 entering the air vents of the metallic mold is to adhere to the lead frame la side only not to the metallic mold side due to the reinforced adhesion of the resin 5 and the lead frame 1a so that the air vents of the metallic mold may not be blocked up with any residual resin 5 thereby ensuring the air discharging function.