To provide a chair that facilitates switching between a reclining position and an upright position, as well as achieves simple and inexpensive production of a sitting part, a backrest, and a sliding structure.

The chair includes: a main frame 1 vertically disposed at both the right and left sides of the chair; a backrest frame 10 pivotally supported at the back of the main frame 1; a seat frame 11 pivotally supported by the backrest frame 10, and configured to protrude forward from the backrest frame 10; and a seat member 14 tightly stretched from the backrest frame 10 through to the seat frame 11, and composing a backrest S and a seat Z.