To obviate a footrest which is formerly necessary for the aged or an invalid to get on and off so that the footrest does not hinder the getting on and off while a patient can be treated keeping the legs stably (comfortably) in both an upright condition and a lying (laying) condition during the dental treatment.

The dental chair has a backrest 12 and a contour seat 13 and the treatment can be executed with the above backrest 12 in the upright condition or the lying (laying) condition. The contour seat 13 has an ankle support (a cylindrical body) 21 at a pointed end which can proceed forward of the contour seat 13 and retreat. In the upright condition, although the legs can be mounted on the footrest 22 which is comprised of the cylindrical body, the getting on and off is not hindered during the treatment. In the lying (laying) treatment, the cylindrical body 21 proceeds forward and the patient can mount the legs (the heels) on it.