PURPOSE: To make an optimum motor control with oscillation and noise minimizes by speed control according to load states of a ventilation fan.

CONSTITUTION: A direct current Ed is obtained from an AC power source 1 via a rectification circuit 2 and a smoothing capacitor 3 and supplied to an inverter controller 4, so that the 3-phase AC output of this inverter controller drives a brushless DC motor 5. A microcomputer 7 outputs a current desired value IDR from a command of a speed command circuit 11 and rotation speed operated from a signal 6s of a magnetic polar position detection circuit 6 into a current control circuit 8. Further, this speed command is updated according to load states, until speed is controlled as commanded by the speed command circuit 11.