To provide a dental treatment chair adjustable at a contour sheet to be fitted even for an adult patient and a child patient.

This dental treatment chair comprises support members 14 and 15 provided at a lower part of the contour sheet 11 to support the sheet 11. The member 14 supports a side of the sheet 11 where the patient sits, and the member 15 supports a tip side of a toe of the sheet 11. The member 14 has a movable support member 16 which is expandably and contractibly extended. The member 16 is moved in the direction of an arrow A or an arrow B to change a flexing point (a) of the sheet 11 so as to adjust the point (a) so as to be moved to a patient's knee. Fig. (A) is a view when regulated for the adult, and Fig. (B) is a view when regulated for the child.