A proximity sensor includes a body, a coil, a cap being cylindrical and having a bottom, a hollow housing, and a ring-shaped sealing member. The body includes the coil bobbin at a first end. The coil is wound around the coil bobbin. The cap is to be placed to a body so as to cover a coil bobbin. The housing includes, at a fist end, a circular-cylinder portion having an opening. The housing is to be placed to the body in such a manner that the cap protrudes from the opening. The sealing member is disposed between the outer peripheral surface of the cap and the inner peripheral surface of the circular-cylinder portion of the housing.