To tremendously improve optical characteristics such as astigmatism by sufficiently relieving residual stress.

An optical pickup lens 15 is an optical element having ≤4 mm maximum length D in the optical axis direction and ≤6 mm maximum length L in the direction perpendicular to the optical axis. After the optical pickup lens 15 is formed by injecting a resin containing a polymer having an alicyclic structure into a mold, it is subjected to heat treatment or wet heat treatment at a temperature lower by 35 to 45°C than the glass transition temperature of the resin for 16 hours or longer, wherein the glass transition temperature is measured by differential scanning calorimetry at a temperature rising rate of 10°C/min based on JIS K7121.