PURPOSE: To achieve a quick detection of the unbalance position without measuring errors by applying a rotation to detect an unbalance signal which a pulse is generated at each specified angle of rotation obtained by equally dividing one cycle of rotation.

CONSTITUTION: An unbalance signal generated with the rotation of a sample W is detected with a sensor 5a (5b) and unwanted frequency components are removed with a filter 11. On the other hand, a reference phase signal generation circuit 12 generates a pulse-like signal synchronizing with an input signal as output of the filter 11. A rotaly encoder 8 measures the rotation of the sample W and generates a pulse signal at each specified angle obtained by equally dividing one cycle. Then, a preset counter 18 receives output and counts outputs of the encoder 8 using output of the circuit 12 as trigger at the constant speed rotation of the sample W and generate an output signal when counts coincide the preset value. Then, a stop device 9 stops the unbalance point of the sample W at the home position by this output signal.