To solve defects such as the inability of a folding chair to be flatly folded due to the considerable difference of the angle of a back rest to leg members, which are opened and closed in an X-shape to the right and left, the protrusion of the backrest forward and to solve the problems of constraints on the shape of the backrest in the right and left directions and difficulties in setting a curved surface for a seat surface with a margin and the cushion properties of the backrest in a folding chair to only fold its backrest to a seat surface.

In a chair supported by lag members 1 to be opened and closed in an X-shape to the right and left, backrest supporting frames 10 are mounted in such a way as to be rotated about an axis in parallel with the direction of the X-shaped opening and closing of the leg members 1. When the leg members 1 are opened, the backrest supporting frames 10 spreads the backrest surface sheet 11 to the right and left to form the backrest of the chair while a seat surface sheet 8 maintains its curved surface. When the leg members 1 are closed, the backrest frames 10 are rotated and folded together with the leg members 1. Similarly, the chair is supported by either the front parts or rear parts of the leg parts 1, and the other is held by a table or a band and integrally constituted.