A device for supplying a patient with breathing gas, which has a housing provided with gas ducts and a corresponding cover (5), shall be improved such that the cover (5) can be manufactured in a simple manner and possesses good sealing properties. To accomplish the object, provisions are made for the cover (5) to consist of a one-piece, plate-like elastomer material and for groove-like depressions (10) extending in the direction of partitions (6) to be present as a seal for the gas ducts (8).