TWI556773B

A reaction mechanism for a backrest of a chair set forth in this invention makes it possible to give the bottom of the chair a streamlined look and frees up greater space under the chair, while utilizing a longer reaction spring than those of existing mechanisms of the same type. The reaction mechanism for the backrest of the chair has a base member (2) supported by a leg (1), a back support member (4) supporting a backrest (3) connected to said base member (2) via a rotating shaft (7) reclinably connected, a seat support member (6) fitted with a seat (5), a body-weight accommodating counterforce mechanism that raises the seat support member (6) in a coordinated motion when the back support member (4) is reclined, and a counterforce spring (16) that applies spring force to return the back support member (4) to its original position, wherein said reaction spring (16) is positioned transversely between the back support member (4) and the seat support component (6).