Transfer device for the motor handicapped, comprising a transferable seat assembly for the motor handicapped, in particular a passenger, comprising at least one movable, transferable, possibly upholstered, horizontally movable upper part or seat proper (1, 1") on which the user sits, having a front edge, a rear edge and two side edges, at least two fixed lower parts (2, 2', 2") fixable respectively to the seats or supports (23, 24, 25, 26, 38, 44, 47) between which the transfer is to be provided, said lower parts (2, 2', 2") each having a front edge, a rear edge and two side edges, and comprising, on their upper face, guiding means (13, 17) for the displacement of the upper part (1, 1") thereon essentially in a direction substantially perpendicular to said side edges, and thus to the sagittal plane of the passenger sitting on said transferable upper part (1, 1"), said guide means (13, 17) cooperating with complementary guide means presented by the lower face of said upper part (1, 1"), characterised in that: - said guiding means allow for play in both the vertical and transverse directions, - one of the upper or lower parts has rolling means distributed over its surface outside the guide means, allowing the seat to roll horizontally with respect to the said lower part and supporting the weight of the seat (1, 1"), so that, when the parts (1, 1", 2, 2', 2") are in a horizontal or slightly inclined position, the guide formed by the said guide means (13, 17) is only slightly or not at all stressed by the weight of the user, and - said lower parts (2, 2', 2") are plate-shaped. at least one movable, transferable, possibly upholstered, horizontally movable upper part or seat proper (1, 1") on which the user sits, having a front edge, a rear edge and two side edges, at least two fixed lower parts (2, 2', 2") fixable respectively to the seats or supports (23, 24, 25, 26, 38, 44, 47) between which the transfer is to be provided, said lower parts (2, 2', 2") each having a front edge, a rear edge and two side edges, and comprising, on their upper face, guiding means (13, 17) for the displacement of the upper part (1, 1") thereon essentially in a direction substantially perpendicular to said side edges, and thus to the sagittal plane of the passenger sitting on said transferable upper part (1, 1"), said guide means (13, 17) cooperating with complementary guide means presented by the lower face of said upper part (1, 1"), characterised in that: - said guiding means allow for play in both the vertical and transverse directions, - one of the upper or lower parts has rolling means distributed over its surface outside the guide means, allowing the seat to roll horizontally with respect to the said lower part and supporting the weight of the seat (1, 1"), so that, when the parts (1, 1", 2, 2', 2") are in a horizontal or slightly inclined position, the guide formed by the said guide means (13, 17) is only slightly or not at all stressed by the weight of the user, and - said lower parts (2, 2', 2") are plate-shaped. - said guiding means allow for play in both the vertical and transverse directions, - one of the upper or lower parts has rolling means distributed over its surface outside the guide means, allowing the seat to roll horizontally with respect to the said lower part and supporting the weight of the seat (1, 1"), so that, when the parts (1, 1", 2, 2', 2") are in a horizontal or slightly inclined position, the guide formed by the said guide means (13, 17) is only slightly or not at all stressed by the weight of the user, and - said lower parts (2, 2', 2") are plate-shaped.