Abstract: A benzylamine derivative has a structure represented by the following formula (1): In a method for optical resolution of the benzylamine derivative, optically active mandelic acid is used as an optical resolving agent. In an optical resolution step in a production method of the optically active benzylamine derivative, an optically active (S)-benzylamine derivative represented by the formula (3) is precipitated as (S)-mandelic acid salt from a solution containing the benzylamine derivative and (S)-mandelic acid: wherein Ar represents an aryl group that has 6 to 15 carbon atoms and may have a substituent, and *1 represents an asymmetric carbon atom.