Abstract: A support device provided to be arranged on a base member (1) such as a mattress, a bunk or a bed, and comprising an inflatable portion (2) which is arranged to be in an inflated state in order to lift a person resting upon the inflatable portion (2), the inflatable portion (2) comprising an inlet opening (5) and an outlet opening (6) for the supply and evacuation respectively of an inflation medium. The inflatable portion (2) comprises a lateral projection (4) provided to project beyond a lateral edge (3) of the base member (1) and at which the inlet opening (5) and the outlet opening (6) are arranged.