Abstract: In a sealing device for a filling opening, especially for sealing it against the escape of fuel fumes when filling stationary or mobile supply tanks, a seal is located in the vicinity of the filling opening and abuts in a sealing fashion an object such as a filling device that is inserted into the filling opening. The seal automatically controlled by means of a control unit between an inactive resting position and an active sealing position of the seal. As a result, the seal is protected especially well against damage during insertion or withdrawal of the filling device, and reliable sealing can be expected in the long term.