The invention relates to a device for supporting a body or part of a body, in particular a human body, said device comprising a support element (2) including a seat (3) and a peripheral sidewall (4), such as to define a housing (5) having a bottom (6) and a peripheral side face (7), and a pneumatic element (9) comprising a base (10) and inflatable cells (11) fitted inside the housing (5) and extending between the bottom (6) of the housing and the base (10) of the pneumatic element (9). According to the invention, the peripheral sidewall (4) comprises at least one inner retaining bead (8) at a distance from the bottom (6) of the housing (5), and, when inflated, at least some of the inflatable cells (11a) adjacent to the retaining bead (8a) can be engaged laterally between the retaining bead (8) and the bottom (6) of the housing (5).
