PURPOSE: To detect a position with extremely high reliability by detecting back electromotive force and detecting an access to a predetermined position.

CONSTITUTION: A control section 1 controls a stepping motor 4 through a drive circuit 2 and a phase excitation control circuit 3. A back electromotive force detection circuit 5 detects back electromotive force generated when 1 driven body transferred by the revolution of the stepping moter 4 driven by a drive means is brought into contact with a stopper and the stepping motor is rotated reversely at a stable position determined by the subsequent exciting phase of the stepping motor, thus detecting an access to a prescribed position. Accordingly, a position sensor, which need not use a photosensor and a microswitch for detecting the prescribed position, in which un neccssary signal conductors need not be drawn around and which has simple constitution and extremely high reliability, is acquired.