To prevent malfunctions with noise superimposed on a control signal pattern by detecting the combination of signal level with one signal level change for detecting magnetic pole position of a rotor magnet and inhibiting the drive of a motor, when such a combination is mismatched with a plurality of predetermined combinations.

A control circuit 3 monitors, when a fan motor 10 is driven, signals Hu to Hw from the Hall Ics 11u 11W and determines the combination pattern in the level of input signals Hu to Hw with change of signal level. Moreover, the control circuit 3 checks whether or not the pattern of determined signals Hu to Hw includes a preset pattern. When a pattern is included, a control signal is output to the drive circuit 2 to turn on only preset transistor 21u to 21z for each pattern, in order to control the drive of fan motor 10. Moreover, the combination of a control signal level is classified into six patterns, and the combination of output control signal level is also classified into six patterns. Thereby, the malfunctions due to the noise superimposed on the signal of each sensor can be prevented.