Abstract: In a vibratory parts feeder, an output power of an inverter supplying AC voltage to each vibration generator (electric power supplied to the vibration generator) or input power to the inverter is controlled so as to reach the maximum during the feeding operation so that the operational frequency is automatically adjusted to the resonant frequency. That is, upon increase or decrease of the operational frequency at predetermined intervals, the value of power supplied to each vibration generator or the inverter input power is obtained. The obtained value is compared with the last obtained value whose data is stored in a storage.