A chair includes a lower structure configured to be placed on a floor surface (F), a backrest support member supported by the lower structure body, and a backrest supported by the backrest support member. The backrest includes a backrest body fixed to the backrest support member and provided with an opening portion (S2) that opens downward, and a tensile material provided in the backrest body and having a lower end portion that is locked on the backrest body. The backrest body includes a plate-shaped backrest main body fixed to the backrest support member and provided with a load-supporting surface that supports a load of a seated person. The backrest support member is inserted into the opening portion of the backrest body and is disposed on a rear side of the backrest main body.