Abstract: The chair can be converted from a state where a person traditionally sits on the approximately horizontal seat (13) of the chair to another state where the person sits on the now inclined seat of the chair, one and the same means being used as back rest in one state and as knee rest in another state. The combined back and knee rest is arranged on one end of a two-armed lever (16) on whose other end there is provided a shaft (18) which is movable in a U-shaped guide (19) in firm connection with the seat. This ensures simple and rapid conversion of the chair between its two states.