Abstract: A shut-off device particularly suitable for implantations in the urethra provided with a tubular housing having attaching means for permanent fitting on the wall tissue of the urethra, a valve system for closing off and making free the passage in said housing and means for disconnectably coupling said valve system in said housing, said valve system consisting of a cylindrical element wherein are arranged a valve seat having a valve co-operating therewith and magnetical means for pressing said valve and seat against one another, whereby the opening pressure can be determined by exerting downward pressure or by having the patient apply manual pressure to the abdominal wall.