PURPOSE: To make it possible to adjust the folding angle between a root panel and an intermediate panel, by forwardly extending both side sections of the root panel attached rotatably to a hull and, by suspending a wedge rotatably to the tip end of the root panel so that the inclination of the wedge may be adjusted.

CONSTITUTION: Side beams 4 are laid on both forwardly extended sections of a root panel 1 coupled rotatably to a hull by means of a pivotal shaft 11. A wedge 20 is rotatably suspended to the tip end of the side beams 4 inside thereof. The inclined position of the wedge 20 is limited by a pin fitted in one of stopper holes 25 formed in the side beam 4. With this arrangement, the lower end of the wedge 20 abuts against the upper surface of an intermediate panel 2 so that the folding angle between the root panel 1 and the intermediate panel 2 may be adjusted by selecting the inclined position of the wedge 20, thereby the attaching level of the ramp may be suitably adjusted and held.