A sensor housing has a receiving recess at one end portion of the sensor housing located at one end of the sensor housing. The one end portion of the sensor housing faces first and second magnetic circuit portions. A circuit board is received in the receiving recess and has an opening, a front-side region and a rear-side region. The front-side region is located on a side of the opening where the one end of the sensor housing is placed. The rear-side region is located on an opposite side of the opening. A main body of a magnetic sensing device overlaps the opening such that terminals projecting from one of a pair of side walls of the main body are located at the front-side region, and terminals projecting from another one of the pair of side walls is located at the rear-side region.