A magnetic flux emission unit is mounted on a detection object and rotatable integrally with the detection object. An IC package includes a magnetism detection element, which sends a signal according to change in a magnetic flux caused when the magnetic flux emission unit rotates. A cover member includes a bottom portion and a tubular portion. The tubular portion is extended from an outer periphery of the bottom portion. The cover member surrounds the magnetic flux emission unit with the bottom portion when mounted to the housing. A support portion is projected from the bottom portion toward an opening of the tubular portion to support the IC package. A projection is projected toward the opening from the bottom portion to at least a position corresponding to the magnetism detection element.