Abstract: In a coin discriminating apparatus containing a feedback oscillator circuit having a feedback loop, a mechanical filter is arranged and includes a discriminated coin, a speaker to vibrate the coin and a sensor to pick up the vibration of the coin; a one cycle selector for taking out one period of the vibration frequency generated at the oscillator circuit; means for quantizing the output signal of the one cycle selector by clock pulses; counter means including a scale-of-1000 counter and a decoder for counting the number of clock pulses; and bistable circuit means whose state is reversed on receipt of an output produced at the decoder when contents of the counter run up to the lower limit or the upper limit of a tolerance predetermined under the crossing rate distribution for natural frequencies of a genuine coin.