The position detecting device of the present invention is a device for detecting the position of a movable detection target within a predetermined movable range. The position detecting device comprises: a first magnet (13A) and a second magnet (13B) which are arranged so as to move integrally with the movement of the detection target; a first magnetic detecting circuit (20A) that detects the magnetic field of the first magnet (13A) and a second magnetic detecting circuit (20B) that detects the magnetic field of the second magnet (13B), which are arranged at positions outside the movable range; and a differential amplifier (8) that amplifies the difference between the detection signals of the magnetic field output from the first magnetic detecting circuit (20A) and the second magnetic detecting circuit (20B), and that outputs the amplified difference of the signal as a position detecting signal of the detection target.