Patent ID: 8317270

Claim:
A backrest device for a chair comprising: a pair of lateral pipe units spaced apart from each other along a left-right direction, each of said lateral pipe units including: an upright backrest mounting pipe member having a hollow main surrounding wall that has, a middle segment, and a pair of symmetric extending segments extending respectively from opposite circumferential ends of said middle segment and cooperating with said middle segment to define a surrounding space thereamong; a groove-defining wall that is disposed in said surrounding space, that has a convex configuration facing toward said middle segment of said main surrounding wall with opposite ends thereof connected respectively to said extending segments of said main surrounding wall, that extends from an upper end toward a lower end of said main surrounding wall, and that defines an engaging groove therein; a coupling pipe member having a coupling surrounding wall that is coupled to said lower end of said main surrounding wall of said backrest mounting pipe member; an abutting wall that is disposed to close a top end of said coupling surrounding wall; a backrest unit including a backrest member having opposite lateral portions, each of which forms a rod-receiving loop; a pair of positioning rods sleeved respectively in said rod-receiving loops; and each of said lateral portions of said backrest member and a respective one of said positioning rods being retained within said engaging groove of said backrest mounting pipe members of a respective one of said lateral pipe units and abutting against said abutting wall of said coupling pipe member of a corresponding one of said lateral pipe units.