To provide a lens array which has heat resistance and excellent resolution, and to provide a rod lens used for the lens array.

The plastic rod lens is produced by polymerizing a mixture of at least one transparent resin polymer (A) selected from polymethylmethacrylate (PMMA), polystyrene (PSt) and a methylmethacrylate-styrene resin (MS resin), and a monomer (B) essentially comprising isobornylmethacrylate, in which the proportion of isobornylmethacrylate in the whole polymer within a range from 0 to 0.8r of the rod lens, from the center to the periphery, is set 10 to 60 parts by mass. The obtained rod lens shows a change rate in a conjugate length of within 6% under the conditions of at 80C for 1,000 hours.