Seat position sensor

The seat position sensor includes a housing (1), a magnetoelectric converting element (4) which performs changeover of an output at a given magnetic field intensity, and a magnet (7) which is held by the housing at a position where the magnet (7) faces the magnetoelectric converting element (4) in an opposed manner. A shielding plate (14) is capable of entering into or exiting from a space defined between the magnetoelectric converting element (4) and the magnet (7). An inverse bias magnet (6) which applies a magnetic field of an inverse direction to the (7) magnet is provided to a side opposite to the magnet (7) side while sandwiching the magnetoelectric converting element (4) therebetween.