Abstract: A chair comprising a box type stationary frame fixed to an upper end of a pole brace erected on leg portions, an L-shaped back rest frame whose lower portion is curved, a base frame for mounting a seat plate, an inclination adjusting mechanism for controlling an inclination of the base frame and the reclining frame to an optional angle in which the reclining frame is axially fixed to a rear portion of the stationary frame and the reclining frame is axially fixed to a rear end portion of the base frame at its curved portion, a horizontal shaft axially supported on a front portion of the base frame and inserted through an almost horizontal long hole provided in the front part of the stationary frame, a gas spring one end of which is pivotally fixed to an inside wall of the stationary frame and the other end of which is pivotally fixed to the horizontal shaft, and an operation lever for switching a push valve of the gas spring, and said operation lever being provided with a lever releasing keeping mechanism for