Abstract: A chair is equipped with a leg column 1, a seat 3, and a back support 4. An intermediate supporting member 9 is fitted to an upper end of the leg column 1, the seat 3 and a back frame 5 are fitted to the intermediate supporting member 9, and the back support 4 is fitted to an upper end of the back frame 5 via a joint unit 11. The seat 3 has an elongated shape when viewed from the top, and is fitted to the intermediate supporting member 9 to swivel horizontally. The back support 4 can be turned freely around a first axis 13 and also can be turned freely around a second axis 12. Since the seat 3 and the back support 4 can be changed into various modes, a using mode of the chair can be changed variously.

Abstract: An ergonomical chair is provided, of the type which is adjustable in height, whose seat has a front portion with a slope automatically changeable as a function of the height adjustment. The seat rear portion remains substantially horizontal, irrespective of the height adjustment and the consequent tilting of the front portion, thus avoiding the downward sliding of the body which can stay in its erect or slightly backward bent position, while a correct leaning of the seat front portion of the lower region of the thighs is ensured without exerting any tiring action by the user. Another embodiment of the invention has armrests and backrest adjustable integrally with each other.

Abstract: An ergonomic chair has its seat portion (4) which, in addition to be adjustable as to the height, forms a variable tilting angle, positive or negative with respect to the horizontal, in consequence of the height thereof, said tilting angle being obtained through a swinging movement of the seat (4) such as to form an arc of circumference about a rotation center substantially coincident with the center of gravity (CG) of a person sitting on the chair. This swinging movement of the seat is preferably accompanied by the rotation of a lever arm (6) pivotedly mounted at an end (6a) to the stationary portion (1a) of the seat support (1) and hinged at the other end (6b) to the front side of the seat (4), the length of said lever (6) or the pivoting point with seat (4) being adjustable by a simple operation of the user to modify the variation of the tilting angle of the seat (4) in function of its height. Said lever arm (6) may be provided with some elastic feature.