A seat suspension which is provided with a lower frame mounted on a vehicle body floor, an upper frame mounted on the lower frame via a link so as to be movable vertically and supporting a seat, and a spring mechanism supporting the upper frame resiliently, wherein the spring mechanism comprises a combination of a magnetic spring having a negative spring constant in a predetermined displacement range and a resilient member having a positive spring constant; the magnetic spring is provided with a fixed magnet unit which is supported by one of the side of the upper frame and the side of the lower frame and a moving magnet unit which is supported by the other thereof; the fixed magnet unit is provided with a fixed side magnet supporting frame and a fixed side magnet provided on the fixed side magnet supporting frame so as to have magnetic poles facing each other; the moving magnet unit is provided with a moving body composed of a magnet which is movable between the magnetic poles facing each other in the fixed side magnet in a direction perpendicular to a facing direction of the magnetic poles; and the upper frame and the lower frame are coupled to each other by a first link arranged on a front side and a second link arranged on a rear side, two torsion bars (31, 41) each serving as the resilient member having a positive spring constant are provided at two coupling portions between the first link and the upper frame and between the second link and the upper frame, or two coupling portions between the first link and the lower frame and between the second link and the lower frame, and an initial position adjusting member which can adjust initial resilient forces of the two torsion bars (31, 41) together is provided, wherein the initial position adjusting member is provided with two adjustment-operating members (16, 17) connected to the respective torsion bars (31, 41) and a shaft coupling the two adjustment-operating members (16, 17), and according to movement of a movable plate of one of the adjustment-operating members, a movable plate of the other of the adjustment-operating members can also be moved. the spring mechanism comprises a combination of a magnetic spring having a negative spring constant in a predetermined displacement range and a resilient member having a positive spring constant; the magnetic spring is provided with a fixed magnet unit which is supported by one of the side of the upper frame and the side of the lower frame and a moving magnet unit which is supported by the other thereof; the fixed magnet unit is provided with a fixed side magnet supporting frame and a fixed side magnet provided on the fixed side magnet supporting frame so as to have magnetic poles facing each other; the moving magnet unit is provided with a moving body composed of a magnet which is movable between the magnetic poles facing each other in the fixed side magnet in a direction perpendicular to a facing direction of the magnetic poles; and the upper frame and the lower frame are coupled to each other by a first link arranged on a front side and a second link arranged on a rear side, two torsion bars (31, 41) each serving as the resilient member having a positive spring constant are provided at two coupling portions between the first link and the upper frame and between the second link and the upper frame, or two coupling portions between the first link and the lower frame and between the second link and the lower frame, and an initial position adjusting member which can adjust initial resilient forces of the two torsion bars (31, 41) together is provided, wherein the initial position adjusting member is provided with two adjustment-operating members (16, 17) connected to the respective torsion bars (31, 41) and a shaft coupling the two adjustment-operating members (16, 17), and according to movement of a movable plate of one of the adjustment-operating members, a movable plate of the other of the adjustment-operating members can also be moved.