A rotational angle sensor and a connector are provided at a first-side portion and a second-side portion, respectively, of a sensor holder. The first-side portion is engaged with a base through a primary engaging arrangement, and the second-side portion is engaged with the base through a secondary engaging arrangement. The secondary engaging arrangement includes secondary engaging portions of the sensor holder, which are provided in the second-side portion of the sensor holder and are engaged with the base. A distance from an engaging point between the secondary engaging portion of the sensor holder and the base to the sensor is longer than a distance from the engaging point between the secondary engaging portion of the sensor holder and the base to the connector.