PURPOSE: To exhibit good surface hardness after mold releasing, to provide a reflection preventing film with good adhesiveness and consisting of an inorg. substance on the surface and to make high productiity and high quality possible.

CONSTITUTION: In a method for cast polymerization using a glass-made mold for casting, a film consisting of a polymerizable hard coat for forming an org. crosslinkable polymer body is formed on the inner face of the glass mold in advance. All the problems such as a plastic lens with low surface hardness, a plastic lens with poor peeling off properties with the glass mold and a hard coat with no adhesiveness with a reflection preventing film consisting of an inorg. substance can be thereby solved and a lens product with high qualities can be obtd. and manufacturing with good efficiency can become possible.