PURPOSE: To make it possible to decrease the number of the parts of the position detecting circuit of a rotor and to make it possible to decrease the number of the lines of position detecting signals.

CONSTITUTION: This is the method for detecting the position of the rotor of a brushless motor for detecting the position of the rotor of the three-phase brushless motor. When the conduction of the armature winding of the brushless motor 1 is switched on the basis of the position detection of the rotor 1a of the brushless motor 1, the terminal voltage of the armature winding of the brushless motor l is inputted into a position detecting part 7, and two position detecting signals are obtained. The two position detecting signals are inputted into a control circuit 8. The control circuit 8 detects the rising and falling edges of the two position detecting signals, measures the time between the edges and estimates the other position detecting signal on the basis of the measured time and the edge timing of the position detecting signal.