To provide a planar lens which is made of a transparent thermoplastic hydrocarbon resin, is excellent in mechanical strength and is small in impact resistance, moldability and hygroscopic deformation and a manufacturing method.

The thermoplastic hydrocarbon resin of this planar lens consisting of the thermoplastic hydrocarbon resin contains ≥30 wt.% repeating unit having an alicyclic structure and ≥30 wt.% repeating unit having the alicyclic structure not having the norbornane ring in the repeating unit having the alicyclic structure. The process for producing the planar lens made of the thermoplastic hydrocarbon resin includes a stage for forming such thermoplastic hydrocarbon resin to a sheet by a melt extrusion method and stage for forming the planar lens by compression molding of the sheet obtd. by the stage.