To provide a chair which is perfectly contained in a wall surface without projections/recessions at the time of non-usage and also where height is adjustable.

A rack plate 30 where a rack 31 is formed in a vertical direction and guide grooves are formed in the neighborhood of both sides in a left and right direction is fixed to the deep wall of containing space B formed in a wall surface A. A slide plate 20 mounted on the rack plate 30 so as to be freely elevating/lowering possible is provided with a pair of bearings 21 and 21 on a front surface and a square window 26 in a lower part. The seat surface support plate 12 of a seat surface 10 is fitted to the slide plate 20 by a pin 22 so as to be elevating/declining possible. The rack engaged with the rack 31 of the rack plate 30 through the square window 26 of the slide plate 20 is formed on the end surface of the seat surface support plate 12 which projects from the seat surface 10. A gap made between the lower end of the seat surface 10 in a containing state and the lower end of containing space B is blocked by a blind plate 40 which is fitted to the front lower edge of containing space B.