To prevent rotary control from being hindered, even when the position of a rotor of a brushless motor can not be detected, by changing over current application.

An induced voltage generated in the armature winding of a brushless motor 4 is compared with a reference voltage, and the current of an armature winding is changed over. A control circuit 11 measures and stores the time ta of position detection of a rotor 4a, calculates the time TA of position detection interval by the stored position detection time ta and the preceding position detection time tb, forecasts the current application changeover time tk after the position detection time, from the position detection time and the time of position detection interval, and forecasts the position detection time taa after the time tk. When the position detection of a rotor 4a is not present until a specified time has passed in reference to the forecast current application changeover time tk after the current application of the armature winding is changed over at the forecast current application changeover time, the current application is changed over after the specified time has passed. The forecast time taa is regarded as the time when the position detection has been performed, and stored. The same processing is performed afterwards.