Patent ID: 7372258

Claim:
A rotation detection device, comprising: a magnetism detection unit for a detection of a rotation of a detection object which is magnetic; a magnet for applying a magnetic field to the magnetism detection unit, the magnet having a substantial cylinder shape; a connection member for electrically connecting the magnetism detection unit with the exterior; a sensor body member having a mounting portion which protrudes from a mounting-portion protrusion surface of the sensor body member, and a joint portion which is positioned around the mounting-portion protrusion surface, the magnetism detection unit being fixedly mounted to the mounting portion and electrically connected with the connection member, the magnetism detection unit and the mounting portion of the sensor body member being arranged in the magnet; and a cover member which is bottomed and has an opening at an opening end thereof, the opening end of the cover member being joined to the joint portion of the sensor body member in such a manner that the magnet is housed in the cover member and the mounting-portion protrusion surface is covered by the cover member, wherein: the magnetism detection unit senses a variation of the magnetic field due to a rotation of the detection object so that the rotation of the detection object is detected; and the opening end of the cover member has a joining surface which is joined to a joining surface of the joint portion of the sensor body member, one of the joining surfaces having at least one of a flange-shaped portion and a bent portion, an other of the joining surfaces having a shape corresponding to that of the one thereof, the flange-shaped portion circumferentially protruding outwards from the cover member or the sensor body member.