Abstract: In a chair (1) and a backrest (30) for the chair of the invention, thin back plate extension parts (51) that are continuous with a front surface of a back plate part (31), thinned sections being formed in outside portions, in a width direction of the backrest, on the rear surface side; and reinforcing ribs (52) that protrude from inside end parts of the back plate extension parts (51) in the width direction of the backrest to a rear side are provided in regions of side edge support parts (32) above parts where fitting holes (33) are formed. The reinforcing ribs (52) extend substantially in an upward-downward direction, gradually increase in cross-sectional area on a bottom end side, are connected to the parts where the fitting holes (33) are formed.

Abstract: In a chair (1) and a backrest (30) for the chair of the invention, thin back plate extension parts (51) that are continuous with a front surface of a back plate part (31), thinned sections being formed in outside portions, in a width direction of the backrest, on the rear surface side; and reinforcing ribs (52) that protrude from inside end parts of the back plate extension parts (51) in the width direction of the backrest to a rear side are provided in regions of side edge support parts (32) above parts where fitting holes (33) are formed. The reinforcing ribs (52) extend substantially in an upward-downward direction, gradually increase in cross-sectional area on a bottom end side, are connected to the parts where the fitting holes (33) are formed.

Abstract: An armrest device for a chair includes a lower support rod that rises at a side of a chair seat and has a tubular upper end portion; and an upper support cylinder that has an armrest provided in an upper end thereof, is externally fitted to the lower support rod so as to be slidable in an up-down direction, and has a plurality of engaging portions therein. The armrest is made height-adjustable with respect to the lower support rod by disposing the locking member and a biasing member at an upper end portion of the lower support rod and providing the rotating rod inside the lower support rod.

Abstract: A lumbar support on a chair comprises a lumbar support body in which a vertical width gradually becomes smaller from right and left ends to the middle; four mounting portions spaced apart from each other vertically on the lumbar support body and moving vertically along a guide on each of the pair of side frame rods and an operating member connected to each of the mounting portions on the lower edge.

Abstract: An armrest device for a chair includes a lower support rod that rises at a side of a chair seat and has a tubular upper end portion; and an upper support cylinder that has an armrest provided in an upper end thereof, is externally fitted to the lower support rod so as to be slidable in an up-down direction, and has a plurality of engaging portions therein. The armrest is made height-adjustable with respect to the lower support rod by disposing the locking member and a biasing member at an upper end portion of the lower support rod and providing the rotating rod inside the lower support rod.