PURPOSE: To cause the upper portion of the chair in the title to always point forwards by disposing the turning portion of the chair in such a manner that the center of gravity of the turning portion locates in front of or behind the shaft core of a rotary shaft, and providing the chair in such a manner that the upper portion of the shaft core of the rotary shaft is inclined to the direction of the center of gravity of the turning portion.

CONSTITUTION: While the chair in the title is made to point forwards, a flange 5 and a rotary shaft 6 are disposed at some distance from and behind the point G of the center of gravity of the turning portion of the chair, and besides, the upper portion of the shaft core X of the rotary shaft 6 is inclined by αdegrees to the direction of the point G of the center of gravity. A complete rotation of the rotary shaft 6 causes the points G' and G to locate at the top position and the lowest position of the center of gravity, respectively, so that the turning portion in its free state is made to point to the point G, at which it is most stable because of its positional energy; i.e., the chair always points forwards while in its free state.