The car seat has a backrest whose frame (24) accommodates a lumbar support. This comprises an elastic distorting panel (6), which can assume a convex-curved position towards the front. The deg. of curvature is adjustable without noticeably modifying the position where curvature is greatest in relation to the frame, using an auxiliary support (15), to which the plate is coupled at the bottom and hinging on a transverse axis (14) level with the point where curvature is greatest, the support being below the level of the axis. A second auxiliary support is attached to the top of the plate and also hinges on the transverse axis. The adjusting mechanism turns the supports simultaneously and in opposite directions.
