To improve the easiness in the seating and unseating motions of an occupant and secure smooth operations.

A body 12 of a seating/unseating aid tool is made rotatable between the upright bucket position and the prostrated aux. position. The mounting/removing direction of an approx. C-form clip (locking means) 36 whose open end 36a can be spread elastically is made identical to the locus of the motion of a lock bar (part to be held) in follow-up after the rotation of the body 12, and protrusive mounting and fixation on/to the base plate 20 of the body are made while the upright bucket position of the body is used as its holding position.