PURPOSE: To prevent a switching circuit and a brushless motor from being damaged due to excessive current.

CONSTITUTION: The current to a three-phase bridge circuit 13 for performing the conduction control of a brushless motor 15 is detected by a current detection means 16 and the detected current ID is compared with a first current-limiting set value IR1 of a current-limiter means 26 and a second current-limiting set value IR2. Then, when the detected current ID is equal to or larger than the first current-limiting set value IR1, a base drive circuit 30 is controlled by a latch means 29 to turn off transistors 7 and 9 at the positive side of the three-phase bridge circuit 13. Further, when the detected current ID is equal to or larger than the second current-limiting set value IR2, the base drive circuit 30 is controlled by the latch means 29 and all transistors 7 and 12 of the three- phase bridge circuit 13 are turned off.