The invention relates to a connecting device (1) for detachably connecting two assemblies (4, 5), said connecting device comprising a closure module (2) which is associated with a first of the assemblies (4, 5) and has: a housing assembly; an adjusting element (22) adjustably mounted on the housing assembly; and a vacuum element (27). An attachment assembly (3) is associated with a second of the assemblies (4, 5) and has an attachment part (30), it being possible for the closure module (2) and the attachment part (30) of the attachment assembly (3) to be attached to one another along an attachment direction (A) so that, in a connected position when the first and second of the assemblies (4, 5) are loaded with respect to one another, the closure module (2) is held against the second of the assemblies (4, 5) as a result of a vacuum effect brought about by the vacuum element (27). The attachment part (30) of the attachment assembly (3) is designed to be adhesively bonded to the second of the assemblies (4, 5).