A method of discriminating coins by use of a pair of oval sensor coils (17, 17′) opposedly arranged at both sides of a coin passage (33) in a coin acceptor with the longitudinal axis of the coils extended along a coin guide rail (34) in the coin passage is disclosed. The method comprises steps of detecting a variation of coil reactance caused by a coin rolling on the guide rail (34), counting clock pulses in a pass time from a start point to a final point of the variation of coil reactance, reading the whole variation of the coil reactance from the start point to the final point thereof by a microcomputer (39), providing a plurality of variation divided data by dividing the pass time by an integral number and comparing the variation data with corresponding reference data of genuine coin or coins previously stored in the microcomputer (39).