An assistance device for people with reduced mobility, notably for allowing a wheeled vehicle to pass over an obstacle, comprising: - a stationary frame, - a vertically movable upper plate, - a lower plate that is mounted for translational movement along an inclined axis with respect to the horizontal between a rest position under the upper plate and a deployed position, the lower plate comprising a body and two raised lateral edges that are disposed along planes parallel to said axis, each raised lateral edge comprising an upper surface, the upper plate being supported at least in part on said raised lateral edges, the deployed position of the lower plate mechanically determining the vertical position of the upper plate, said raised lateral edges also forming a guide for moving the vehicle onto and aligning it on the lower plate, - a flap that is mounted so as to pivot mechanically on the upper plate about a substantially horizontal axis perpendicular to the axis of translational movement of the lower plate, said flap being able to pivot between a substantially vertical rest position and a deployed position resting on the lower plate, said flap forming a junction between the lower plate and the upper plate, said flap being pivoted by said raised lateral edges at least over a part of its pivoting travel, and - a mechanical member (71; 72) for locking the flap in the rest position, said mechanical locking member (71; 72) being supported on said raised lateral edges and being passive with respect to said raised lateral edges, locking said flap in the rest position of the lower plate and releasing said flap when said lower plate leaves its rest position. - a stationary frame, - a vertically movable upper plate, - a lower plate that is mounted for translational movement along an inclined axis with respect to the horizontal between a rest position under the upper plate and a deployed position, the lower plate comprising a body and two raised lateral edges that are disposed along planes parallel to said axis, each raised lateral edge comprising an upper surface, the upper plate being supported at least in part on said raised lateral edges, the deployed position of the lower plate mechanically determining the vertical position of the upper plate, said raised lateral edges also forming a guide for moving the vehicle onto and aligning it on the lower plate, - a flap that is mounted so as to pivot mechanically on the upper plate about a substantially horizontal axis perpendicular to the axis of translational movement of the lower plate, said flap being able to pivot between a substantially vertical rest position and a deployed position resting on the lower plate, said flap forming a junction between the lower plate and the upper plate, said flap being pivoted by said raised lateral edges at least over a part of its pivoting travel, and - a mechanical member (71; 72) for locking the flap in the rest position, said mechanical locking member (71; 72) being supported on said raised lateral edges and being passive with respect to said raised lateral edges, locking said flap in the rest position of the lower plate and releasing said flap when said lower plate leaves its rest position.