To prevent the erroneous detection of the position of the rotor of a brushless motor by removing noise, etc., and, in addition, to accurately detect the position in detecting the position with software by using the terminal voltages of the armature windings of the motor.

In a method for controlling brushless motor, a brushless motor 4 is PWM-controlled by impressing DC power upon the motor 4 by switching the power by means of the transistors in an inverter section 3. A/D-converting sections 10, 11, and 12 sample the waveforms of the terminal voltages of the armature windings of the motor 4 and convert the sampled waveforms into digital data (numerical data). A microcomputer 13 fetches the digital data and, on the other hand, low-pass filters the digital data through numerical and arithmetic processing. At the same time, the microcomputer 13 detects the position of the rotor of the motor 4 by comparing the low-pass filtered values with a prescribed value and calculates the conduction switching timing of the motor 4 by driving the transistors of the inverter section 3 based on the detected position of the rotor.