A shut-off device for a fluid includes a housing conducting the fluid, an inflow opening provided in the housing, an outflow opening provided in the housing, a flow channel formed in the housing between the inflow opening and the outflow opening, and a blocking device arranged in the flow channel. The blocking device has a blocking body receptacle and a blocking body movable in the blocking body receptacle. The flow cross-section for the fluid in the blocking device, and thus in the flow channel, can be changed by moving the blocking body in the blocking body receptacle. A reliable detection of the position of the blocking body is ensured in that an ultrasonic measuring device is arranged in or aligned on the housing such that the position of the blocking body can be determined by means of the ultrasonic measuring device.