PROBLEM TO BE SOLVED: To prevent the driving efficiency of a motor from deteriorating while suppressing fluctuation of torque by comparing a specific input signal to each comparator amplified through an amplifier with other output signals thereby compensating for the delay of a conduction current. SOLUTION: An amplifier 20 for amplifying only one of two output signals H (HU, HV, HW) of respective phase being inputted to respective comparators 17 is inserted. A first comparator 17U compares a signal HU1 multiplied by an amplification factor with an output signal HV of phase V to produce a comparison signal HU2. Other comparison signals are also produced similarly. Consequently, the driving efficiency of a motor can be prevented from deteriorating while suppressing fluctuation of torque by correcting the commutation timing of current flowing through each armature coil 7 (7U, 7V, 7W) to a regular commutation timing thereby easily correcting the mechanical positional shift error between the armature coil and a rotor position detector 8 electrically.
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