To facilitate dental treatment by locating the position of the oral cavity of a patient to a specified position for facilitating the dental treatment by moving the seat section with the patient as he/she remains sitting wherever the sitting position of the patient is when the patient has sat on a chair for dental treatment.

This chair has a seat plate 4, a backrest 3 and the movable seat section 10 on the seat plate 4. The seat section 10 has pressure sensors 1111 to 11mn which detect a pressure distribution when the patient sits. The pressure distribution when the patient sits on the seat is detected, and the seat section 10 is moved in response to the pressure distribution, and a state facilitating the dental treatment is presented by making the oral cavity position of the patient to the backrest 3 uniform. The seat section 10 has a lower seat section 101 which can move in the lateral direction (or the longitudinal direction) on the seat plate 4, and an upper seat section 102 which can move in the longitudinal direction (or the lateral direction) on the lower seat section 101, and has the pressure sensors 1111 to 11mn on the upper seat section 102.