To easily and reliably install a woven sheet 2 in a chair frame.

Meanwhile, a pair of vertical supporting rods 15 are arranged near respective upper frames of a backrest supporting frame 11 and a seating face supporting frame 12 of a chair frame 1, a long tubular part 21 is formed by being sawed in end parts at a horizontal portion and a vertical portion of the woven sheet 2 having a T-shape in a plane view. The woven sheet 2 is installed in the chair frame 1 by inserting the respective long tubular parts 21 inwardly from the outside of the chair frame 1, inserting a locking rod 3 formed with a diameter larger than gaps of the pair of vertical supporting rods 15 in the long tubular parts 21, and locking the long tubular parts 21 with the pair of vertical supporting rods 15. Thus, the woven sheet 2 can be taken out and reinstalled by insertion of the locking rod 3.