To provide a speed controlling method for brushless motors capable of suppressing an exciting force to the vibration of a motor load to be produced by the difference between the motor torque and the load torque, and of performing stable operation surely just after the start of current flowing and in a high-speed operation region.

A current flowing winding control system composed of an induced voltage detecting circuit 6, a current flowing winding switching part 8, and a base drive signal generating part 19 forms current flowing winding data 9, and an average speed controlling system composed of the induced voltage detecting circuit 6, an average speed calculating part 12, an average speed comparing part 14, an average impressed voltage adjusting part 15, an impressed voltage adding part 17, and a base drive signal generating part 19 adjusts an average impressed voltage to be impressed to a compressor 4 and forms average impressed voltage data 16. And an instantaneous speed control system composed of the induced voltage detecting circuit 6, a voltage correcting part 10, the impressed voltage adding part 17, and the base drive signal generating part 19 generates drive signals 20a-20f for a group of semiconductor switching elements 3, and controls the flow of a current to a compressor 4.