Abstract: In a dynamic balancing machine for measuring amount and angular location of unbalance of a rotor piece during rotating the rotor piece by a drive motor, in order to position automatically the unbalance angular location to a predetermined angular position on bearings at a time of detection of the unbalance, a preset counter is used for providing a signal to stop the drive motor. Angular pulses each of which indicates rotation of the test rotor piece over a unit angular extent are generated by a rotary encoder, and phase indicating pulses are formed from the vibration signal from a vibration velocity pickup. After constant rotation of the drive motor, motor speed is reduced by a motor speed reduction signal, and, thereafter, the preset counter begins to count the angular pulses in response to presence of one pulse of the phase indicating pulses.