To provide a resin composition which has resistance to environmental changes and light irradiation for long time and is used for optical elements, to provide an optical element molded from the resin composition, and to provide an optical pick-up device to which the optical element is applied, wherein the deterioration of light resistance and heat resistance is controlled.

An object lens 10 as an optical element of the present invention is obtained by molding a resin composition used for optical elements and obtained by mixing a prescribed alicyclic hydrocarbon-based copolymer with an additive, wherein, when 3 pts.mass of the alicyclic hydrocarbon-based copolymer is dissolved in 100 pts.mass of cyclohexane at 40°C and then further mixed with acetone in an amount of ten volume times the volume of the cyclohexane to precipitate the alicyclic hydrocarbon-based copolymer, the amount of components originated from the alicyclic hydrocarbon-based copolymer and left in the solvents as dissolved components is ≤4 wt.% based on the amount of the alicyclic hydrocarbon-based copolymer, before the alicyclic hydrocarbon-based copolymer is dissolved in the cyclohexane.