BACKREST OF CHAIR

PURPOSE: A backrest of a chair is provided to secure the sufficient deformation of a back frame in case of tilting thereof, thereby supporting the lumber of the user with a sufficient strength and stably bearing the upper body of the user with a constant supporting force. CONSTITUTION: In a chair having a tilting case(12) under a seat(10) and a backrest(14) inclined relative to the seat by a certain angle, the backrest comprises a flexible back frame(24), and a support frame(26) installed at the rear side of the back frame and having a certain strength suitable to support the back frame. The lower end of the back frame is hinged to a support bar(28) connecting between the middle portion of the tilting case and the rear end of the seat. The support frame is hinged to the upper end of the back frame at its upper end. The middle portion of the support frame is first bent near legs of the chair, and then extends toward the seat to be hinged to the middle portion of the seat, thereby being coupled to the front side of the tilting case.