To eliminate ripple components of a reluctance torque which are contained in an induced voltage and avoid erroneous position detection in the position detection of a brushless motor which generates also a reluctance torque.

A DC power supply is switched by a plurality of transistors of a transistor matrix unit 3 and applied to a brushless motor 4 to control the rotation of the brushless motor 4. At that time, in a position detection circuit 10, an induced voltage (imaginery neutral voltage) generated in the non- current-application phase of the motor 4 is obtained by a synthesizer circuit 5a, and the induced voltage is applied to a low-pass filter 10a to eliminate the ripple components of a reluctance torque. The induced voltage is then compared with a reference voltage generated by a voltage generating circuit 5b by a comparison circuit 5c, and the comparison result is outputted to a control circuit 6 as a position detection signal.