The purpose is to achieve size reduction, weight reduction and thickness reduction of a magnetic material detecting device (1). The device comprises a linearly displaceable magnet (12) and a Hall IC (14) for detecting the displacement of the magnet (12). When an iron piece (28) is positioned within a predetermined distance from the main body of the magnetic material detecting device (1), the iron piece (28) is strongly magnetized to attract the magnet (12) so that the latter is displaced toward the iron piece (28). Therefore, when the displacement of a magnet (14) is detected by the Hall IC (14), it is possible to detect the fact that the iron piece (28) has been positioned within the predetermined distance from the main body of the magnetic material detecting device (1).