PURPOSE: To improve size accuracy of the lens by complementing contraction of the plastic lens by placing a thin piece of same material as the lens on the curved face of the plastic lens and heat fusing and press bonding.

CONSTITUTION: The plastic lens 31 molded by injection molding or cast molding is placed in the stationary mold 33 and the plastic thin piece 34 of the same material as the lens 31 is placed on the upper face of the lens 31. And the mobile mold 32 in which the predetermined curved face 32a of the lens is shaped is lowered, heated and pressurized, the plastic thin piece 34 is heated, fused and press bonded. By this, contraction of the plastic lens molded by injection molding or cast molding is complemented, then size accuracy of the plastic lens can be improved.