To provide an amorphous thermoplastic resin and a film or sheet each having high transparency and high heat resistance and a UV-absorbing ability, which can be used in various optical materials which needs to have excellent optical characteristics and well-balanced mechanical strength, molding processability, and surface hardness. An amorphous thermoplastic resin including a UV-absorbing monomer unit and having a glass transition temperature of 120° C. or more, in which the amorphous thermoplastic resin has a light transmittance of 80% or more at 500 nm and a light transmittance of less than 30% at 380 nm.