Chair and backrest for chair

Abstract

In a chair () and a backrest () for the chair of the invention, thin back plate extension parts () that are continuous with a front surface of a back plate part (), thinned sections being formed in outside portions, in a width direction of the backrest, on the rear surface side; and reinforcing ribs () that protrude from inside end parts of the back plate extension parts () in the width direction of the backrest to a rear side are provided in regions of side edge support parts () above parts where fitting holes () are formed. The reinforcing ribs () 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 () are formed. Additionally, a chair () and a backrest () for the chair of the invention are provided with a plate-shaped back plate part () that receives a seated person's load, and a pair of side edge support parts () that are formed integrally with a pair of facing opposite sides of the back plate part () and function as strengthening members. A plurality of openings () for facilitating deformation of the back plate part () are formed in the back plate part (). A curved part () that is curved toward an opposite back plate side extends from one end side of the back plate part (). The openings () of the back plate part () formed in the vicinity of the curved part () are formed in the shape of an elongated hole in the extending direction of the side edge support parts (), and are formed at least in a range covering the curved part ().