PURPOSE: To attain the fixed position stop control with high accuracy by detecting easily the degree of magnetization of a spindle.

CONSTITUTION: A magnetism generator 4 is attached to a spindle 3 of a motor 2 which is driven via an inverter 1. The 2-phase analog signal produced by the generator 4 is received by a magnetic sensor 5. Then the stop position of the spindle 3 is calculated from the synthetic signal of the 2-phase analog signals, and the spindle 3 is stopped at a prescribed position. Furthermore a detector circuit 6 calculates the positive-negative asymmetrical value of the 2-phase signal received from a magnetic sensor 5. Then this asymmetrical value is compared with its prescribed value so that the degree of magnetization of the spindle 3 is easily known. Thus the spindle 3 can be precisely stopped at a fixed position.