To facilitate a dentist's treatment action by preventing the oral cavity position of a patient in the longitudinal direction from being changed when a backrest is moved up and down in a state where the extension/contraction quantity of a headrest to the backrest is changed according to the patient's height.

The dental treatment chair includes: a contour seat 13; the backrest 12 movable up and down relative to the contour seat 13; the headrest 11 provided on the backrest 12; and a headrest extension/contraction adjusting mechanism for adjusting the extension/contraction quantity of the headrest 11 relative to the backrest 12, the contour seat 13 being moved forward and backward according to the upward and downward movement of the backrest 12. The chair further includes a headrest expansion/contraction detection unit which detects an expansion/contraction quantity of the headrest 11; and a control unit which controls the forward/backward movement quantity of the contour seat 13 according to the expansion/contraction quantity of the headrest 11 detected by the headrest expansion/contraction detection unit.