Patent ID: 8251454

Claim:
A backrest of a chair comprising: a back frame including: right and left side frames extending in upward/downward directions; an upper frame extending laterally and linking upper ends of the side frames to each other; and a lower frame attaching lower ends of the side frames to a backrest support adapter protruding upward from a rear part of a seat body in the chair; a baggy stretchable backrest cushion which is inverted to open vertically and is knitted; wherein an upper part of the backrest cushion is air permeable; wherein at least a part of the lower backrest cushion covering the lower frame is non-translucent; an adaptation device for adapting said backrest of the chair, wherein a recess is formed to open rearwards and downwards in the lower frame to be covered with said non-translucent part of the backrest cushion; wherein laterally facing portions in said recess are linked by a connection bar laterally extending to be integrated with the lower frame; wherein a connection member is fitted and fixed to the recess in such a manner that a rear-side lower edge of the connection member is abutted to an upper surface of the connection bar, said connection member includes a front surface and right and left sides; wherein a plurality of fitting grooves which respectively extends in the upward/downward direction and of which lower end opens downwardly are formed to face to each other in the rear surface of the lower frame within the recess and in the front surface of the connection member; and wherein said pair of facing fitting grooves receives therebetween an erected portion of the backrest support adapter, said erected portion having an outer shape.