An assistance device (1) to allow a wheeled vehicle to overcome an obstacle, comprising a frame, (2), an upper plate (4), a lower plate (3) with lateral rims (41), a flap (5) and a locking member (71; 72). The upper plate (4) is supported on the lateral rims (41). By moving in translation between a deployed position and a storage position, the lower plate (3) mechanically determines the height position of the upper plate (4) by sliding on the lateral rims (41). The flap (5) pivots relative to the upper plate (4) between a substantially vertical rest position and a deployed position resting on the lower plate (3). The flap (5) forms a junction between the lower plate (3) and the upper plate (4). The locking member (71; 72) is supported by the lateral rims (41) and locks the flap (5) in the storage position of the lower plate (3) and releases the flap (5) when the lower plate (3) leaves the storage position of same.