PURPOSE: To obtain a casting mold capable of giving highly accurate plastic lens by connecting a regulator for the internal pressure of an annular gasket tube to the inside of the tube.

CONSTITUTION: An annular gasket tube 6 is interposed between a top force 3 and a bottom force 4 to support both the forces 3 and 4 at a given interval for forming a cavity between both the forces 3 and 4, and a ring shaped force 7 for fixing optical axle is fitted on the periphery of both the force 3 and 4. The annular gasket tube 6 is formed by providing a valve 8 to the periphery of a tube made of an elastic material, e.g., soft polyvinyl chloride resin, etc. The valve 8 is inserted into a hole 9 provided in the force 7 for fixing optical axle and a regulator 10 for internal pressure of the tube is connected to the valve 8.