A seat device includes a seatback having a backrest surface, a massage airbag that presses a back of an occupant through the backrest surface by performing expanding operation and contracting operation in the interior of the seatback, an air supply-discharge device that selectively supplies air to and discharges internal air from the airbag based on an internal pressure of the airbag, a displacement device that displaces the backrest surface, a timer that measures an air discharge time of the internal air needed for the contracting operation of the airbag, and a load regulating device that controls operation of the displacement device such that a measured value of the air discharge time approaches a target value of the air discharge time in correspondence with a change of an occupant load acting on the backrest surface due to displacement of the backrest surface.