To surely prevent the hands of a user from being pinched by applying external force directly to a leg, and retreating a coupling member to release the temporarily held state of the leg located at an intermediate position.

The lock pin 21 of a lock plate 14 is retreated from the first coupled section 23 of a shaft plate 7, it is excited by a torsion coil spring 22 and coupled with the second coupled section 24, and a leg 2 is temporarily held at an intermediate position R in a slightly inclined state from a using position. A user himself holds the leg 2 from the rear and prostrates it forward with fixed force to rotate the leg 2 to a storage position. The lock pin 21 is excited by the second coupled section 24, is retreated from the second coupled section 24, and is slid on the inclined face 7c of the shaft plate 7. When the leg 2 reaches the storage position, the lock pin 21 is excited by the torsion coil spring 22 and is coupled with the third coupled section 25, the partial circular arc section 7b of the shaft plate 7 approaches the erect wall 6c of a receiving frame, and the leg 2 is drawn into a lock state at the storage position.