Abstract: A chair back includes a waist support, a board-shaped part, and a mesh member; the board-shaped part has guide grooves on a front side; the mesh member includes a frame, and a mesh secured over a space encompassed by the frame; the mesh member is secured right in front of the board-shaped part; the waist support is sandwiched between the mesh member and the board-shaped part with such a tightness that it can be moved up and down for adjusting position; the waist support has guide protrusions on a rear side thereof, which are fitted in the guide grooves of the board-shaped part; the waist support has two grip portions extending from two ends thereof and sticking out from two lateral edges of the chair back such that the sitter is allowed to adjust the waist support by means of exerting force on the grip portions.