<p>A chair (1) that includes a seat (2) which has a shape similar to that of a horse's saddle and which is supported by a telescopic leg post (3) that includes a bottom rubber-coated ferrule (3a) for engagement with the floor surface. The seat has an outwardly concave upper part (2a) and two downwardly extending and outwardly convave side parts (2b). The lower part (3a) of the leg post (3) has rearwardly and outwardly projecting leg supports (4) whose free ends form support feet (4b) situated on the rear side of the chair. The support legs are so orientated relative to the leg post (3) as to be out of contact with the floor surface when the leg post is vertical or in a forwardly inclined position. The leg post accommodates a gas spring which enables the height of the seat (2) to be adjusted. When the chair is in use, it can be swung to any desired forward position or sideways-inclined position with the aid of the user's legs. The leg post (3) is inclined slightly rearwards in the rest position of the chair.</p>