To provide a structure of attaching a seatback of a chair which enables a user to attach a seatback board made of a synthetic resin to a back pole and to detached the seatback board from the back pole easily.

This structure of attaching a seatback of a chair is used to attach a seatback board 7 to a back pole 6 by joining the back pole 6, which is made of a metal and is placed on both sides of the back of the chair, to a cylinder 10, placed under the both sides of the seatback board 7 made of a synthetic resin. Contact parts 11 which make contact with the outer circumference of the back pole 6 are equipped at the back and the front of the inner circumference of the cylinder 10, and non-contact parts 12 which do not make contact with the outer circumference of the back bar are equipped on the left and right of the inner circumference of the cylinder 10. The cylinder 10 and the back pole 6 are fastened with an attaching means 8 which can be attached and detached.