The invention related to a chair (1) which is tiltable and is possible to lock in an essentially horizontal basic position. The chair (1) comprises a seat cushion (2) and an essentially centrally below the seat cushion (2) arranged support leg (3). It also comprises a joint (8) comprising a first joint part (8a) fixedly connected to the seat cushion (2) and a second joint part (8b) fixedly connected to the support leg (3) and a spring (4) arranged concentrically around the support leg (3), acting between the seat cushion (2) and a in the support leg (3) attached spring support (5). The spring (4) is adapted to straighten up the seat cushion (2) and to provide a counter force to the tilting. The invention is characterized in that the first joint part (8a) comprises a through-going locating hole (9) in which a pin (10) is moveably arranged, where the pin (10) has a first end (10a) which is adapted to vertically be moved into a locking hole (11) arranged essentially concentrically with the center axle (x-x) of the support leg (3) in order to lock the seating cushion in an essentially vertical basic position.