To provide an apparatus for treating a fibrous web, in which a sealing element can be replaced without difficulty, i.e., the replacement may be possible even without dismantling a stabilizer box.

This apparatus for treating a fibrous web such as in particular a paper and/or board web is provided; wherein the fibrous web, on its own or together with at least one supporting belt, e.g. a dewatering belt, press belt, mesh belt and/or the like, is guided over at least one moving or stationary supporting surface; on the side of the fibrous web opposite to such a supporting surface, at least one sealing device is provided, which includes a sealing element which is held in a holder which is arranged in the immediate vicinity of the supporting belt without touching the latter, and it is possible for the sealing element to be guided out of the holder laterally, i.e., transversely with respect to the web running direction.