To enable even a person weakened in physical strength to easily operate a chair and to slowly perform standing-up or sitting-down action.

When a manipulator 81 arranged at an upper surface part 501 of an armrest 5 is pressed in the case that a sitting person is to try to stand up concerning a stand-up supporting chair 1, the valve of a gas cylinder is opened at a seat part pushing-up mechanism 6, and the rear end part of a seat part is started being pushed up by a spring for push-up. Therefore, the person weakened in physical strength can stand up from the chair with the aid of that push-up force. When the manipulator 81 is pressed in the case of sitting on the seat part in the oblique attitude, since the valve of the gas cylinder is opened, the person can sit on the seat part while compressing the spring for push-up. Since the motion of such a seat part is regulated in the speed by the gas cylinder, the standing-up or sitting-down action can be slowly performed.