To reduce a burden of seated/standing operation by inclining the seat surface forward so that the thigh part inclines forward when a person is seated, and arranging the hip receiving surface to receive the hip part of the person by being recessed downward more than the almost horizontal direction to rearward from the middle of the longitudinal direction of this seat surface.

When a person is seated by inclining the seat surface 1a of a seat body 1 forward, a line A connecting a hip point 5 being the thigh part 3 and a knee point 6 inclines forward by, for example, θ°=5 to 15°. The hip receiving surface 8 to receive the hip part 9 of the person by being recessed downward more than the almost horizontal direction to rearward from the middle of the longitudinal direction of the seat surface 1a, is arranged on the seat surface 1a. According to this constitution, a burden of initial operation can be reduced since the center of gravity can be brought onto a standing position reference point (b) in a shallow forward inclining posture of the upper body when the body is moved to a standing-up posture. Since the hip point 5 is set higher than the knee point 6, a raising quantity of the hip point 5 can be reduced to also reduce a burden of the final operation.