A position sensor includes a longitudinally extending permanent magnet member at least two longitudinally extending arc-shaped projecting elements respectively projecting from the opposite ends toward the inside space to confront each other at a distance and a pair of compatible main magnetic sensors disposed in the inside space along the longitudinal axis at an interval so as to generate a pair of output signals when the permanent magnet member shifts along the longitudinal axis. The opposite ends of the permanent magnet member are configured to surround a common inside space and polarized to have opposite magnetic poles so as to provide in the inside space a magnetic field whose magnetic flux density becomes a maximum at a longitudinal center of the inside space and gradually becomes smaller as a position of the inside space shifts from the longitudinal center along a longitudinal axis of the permanent magnet members. The arc-shaped projecting elements are arranged so that the magnetic flux density and each of the output signals can be expressed by a cosine of a shift value from the longitudinal center, and the interval is ¼ of the cycle of the cosine.