A supporting member in a conventional seat device is supported only by torsion bar arm portions positioned at right and left sides of the device. Accordingly, when a large biased load acts on the device, a sufficient roll rigidity is not obtained and both arm portions at the right and left sides rotate simultaneously. Interference with the supporting panel, cushion frame or the like may also occur. Accordingly, a seat pad supporting member supported by a cushion frame provided on a floor is elastically supported on at least one of the front and rear portions thereof to a torsion frame by a torsion bar. The torsion bar is latched, at the torsion bar torque bar portion side, to the cushion frame side. The torsion arm portion side, moreover, is latched to the right and left sides. Finally, the torsion bar arm portion, on both sides, is connected to a connecting member.