Covering device

The device (2) has a planar cover element guided from a closed function position into an opened function position. The cover element overlaps a tank aperture (8) of a tank unit (4) and/or a closure part (10) of the tank unit. A sealing part (12) is closed by a gap (14) between the cover element and the tank unit in the closed function position and extended crosswise or diagonally to the tank aperture and spaced to the tank aperture. The sealing part is arranged at the cover element such that the gap spaced to the tank aperture is closed.