Abstract: The purpose of the present invention is to provide a thermoplastic resin far an optical lens. In order to enable an optical lens designer to use a variety of lenses, the thermoplastic resin should have a low refractive index, a low Abbe number and a water absorption rate similar to that of a polycarbonate resin. The present invention relates to a thermoplastic resin which contains repeating units represented by formula (1), formula (2) and formula (3) and which has a refractive index of 1.510-1.570. In formula (I), R1, R2, R3 and R4 are each independently a hydrogen atom or a hydrocarbon group having 1-10 carbon atoms. In formula (3), n is 1-8, R moieties are each independently selected from among a hydrogen atom or an alkyl group having 1-3 carbon atoms, and R5 and R6 are each independently a hydrogen atom or a hydrocarbon group having 1-10 carbon atoms.