A housing slidably guides a slider, which is driven in response to selection of a shift range of an automatic transmission. Upper and lateral sides of a movable range of the slider are covered with the housing. Thereby, application of hydraulic fluid and foreign objects to guide rails is limited to limit malfunction of the slider. Furthermore, even when the hydraulic fluid and foreign objects adhere to the guide rails, the hydraulic fluid and foreign objects can be collected at ends of the movable range of the slider and can be expelled to an outside of the housing through open ends of the housing.