PURPOSE: To decrease the friction between each bearing part and a body under test and to decrease signal noises by applying a voltage, which offsets the induced voltage caused by the friction between each bearing part and the body under test.

CONSTITUTION: Right and left bearing parts 4 and 5 are insulated from the main part of a frame 1 with an insulator I. Offset-voltage generating circuits 11 and 12, which generate the voltage for offsetting the voltage induced by the friction in rotation of a body under test W, are connected between the bearing parts 4 and 5 and the body under test W. The circuits 11 and 12 offset the static electricity generated by the friction between the body under test W and the bearing parts 4 and 5 when the body under test W is rotated and have the measuring circuit for the induced voltage and the generating and feedback controlling circuit for the offset voltage. The dynamic friction coefficient between the bearing parts 4 and 5 and the body under test W is decreased by the offset of the voltages. The noises caused by the friction are alleviated by the outputs of pickups 6 and 7. The accuracy of the measured value of the unbalance is improved with a dynamic-balance measuring circuit 9.