PURPOSE: To simplify the composition of a circuit, by detecting a desired current monitoring signal by arranging phase current detectors on two phases among three-phases of windings, and by obtaining the rest one-phase as a resultant.

CONSTITUTION: The current monitor 1 of a brushless motor 2 is composed of phase current detectors 3r∼3s as current detecting means for detecting the two-phase winding current of the motor 2, a commutation sensor 5, a current signal selecting circuit 6 for obtaining monitor electric-signal, a plurality of inverter circuits 7a∼7d, adder circuits 8a∼8b, and an average circuit 9. In this case, the residual phase current of the motor 2 is combined with the current of said two phases, and is found. A rotational angle to armature windings r∼t during electrical conduction is found by said commutation sensor 5. Then, the average value of phase current according to the output period of the sensor 5 is found and is led to a current monitor terminal. Then, with the composition of a simple circuit, desired current can be monitored.