A chair comprises a seat frame (10) on which a seat and left and right armrests are mounted, a back frame (21) on which a backrest is mounted, a bottom frame (30) on which legs, supporting the left and right armrests, are mounted, and an assisting mechanism (4). The assisting mechanism comprises a lifting mechanism that connects to the seat frame and the back frame and can lift the same, and a driving member (6) that moves the lifting mechanism up and down. The seat frame and the back frame are connected so that when at least one of the same is raised or lowered the other can be raised or lowered in an integral manner, and the seat, the left and right armrests, and the backrest that are mounted on these frames can be raised or lowered in an integral manner. The driving member comprises a fixed part (7) and a telescoping movable part (8). All four of the seat, the left and right armrests, and the backrest are raised in an integral manner when the seat frame and back frame are raised by way of extending the movable part the same are raised in a substantially horizontal direction at the start of the raising, and, as the raising continues, the forward tilt becomes acute. All of the four are lowered in an integral manner when the seat frame and back frame are lowered by way of contracting the movable part at the start of lowering, the forward tilt is restored while lowering, and as the lowering continues the lowering becomes substantially horizontal.Linvention concerne une chaise comprenant un châssis de siège (10) sur lequel un siège et des accoudoirs gauche et droit sont montés, un châssis de dos (21) sur lequel un dossier est monté, un châssis de dessous (30) sur lequel des pieds, supportant les accoudoirs gauche et droit, sont montés, et un mécanisme dassistance (4). Le mécanisme dassistance comprend un mécanisme de soulèvement qui se relie au châssis de siège et au châssis de dos et peut soulever ceux-ci, et un organe dentraînement (6) qui déplace le mécanisme de so
