A mechanical sealing device and a pump including a mechanical sealing device are described. The sealing device includes a first seal element (11) and a first holder element (12) holding the first seal element. The first seal element (11) forms a first seal surface (13), an opposite backing surface (14) and an outer peripheral surface (15). The first holder element has a support surface (16) and an inner surface (17). A second seal element (21), forming a second seal surface (22), is rotatable in relation to the first seal element around an axis (x) of rotation so that the first seal surface (13) abuts sealingly the second seal surface (22) in a radial plane. An elastomer element (30) is provided between the outer peripheral surface (15) and the inner surface. The opposite backing surface abuts tightly the support surface.