A seat suspension to be interposed between a vehicle body floor and a seat, wherein: the seat suspension comprises a first elastic member having a positive spring constant to bias the seat side in a direction to depart from the vehicle body floor side and a second elastic member with a negative spring constant functioning in a predetermined displacement range, the first and second elastic members being structured to form a dead zone where superposed spring constants of the first and second elastic members become substantially zero in the predetermined displacement range, and to damp input vibrations by operation of the dead zone; characterized in that the seat suspension has an active control mechanism comprising: three pantograph links disposed at equal intervals in a circumferential direction in plan view, wherein the pantograph links have first arms and second arms on the left and the right, and when facing the first arms and the second arms, the left arms substantially form the shape of a less-than sign, and the right arms substantially form the shape of a greater-than sign, sensors configured to detect a relative posture of the seat side to the vehicle body floor, wherein feedback signals of the sensors are transmitted to respective drive parts of the three pantograph links via a control unit configured to individually control the first arms and the second arms of each pantograph link by the drive parts respectively to control the pantograph links corresponding to input vibrations from the vehicle body floor and displace the seat side in six-axis directions. the seat suspension comprises a first elastic member having a positive spring constant to bias the seat side in a direction to depart from the vehicle body floor side and a second elastic member with a negative spring constant functioning in a predetermined displacement range, the first and second elastic members being structured to form a dead zone where superposed spring constants of the first and second elastic members become substantially zero in the predetermined displacement range, and to damp input vibrations by operation of the dead zone; characterized in that the seat suspension has an active control mechanism comprising: three pantograph links disposed at equal intervals in a circumferential direction in plan view, wherein the pantograph links have first arms and second arms on the left and the right, and when facing the first arms and the second arms, the left arms substantially form the shape of a less-than sign, and the right arms substantially form the shape of a greater-than sign, sensors configured to detect a relative posture of the seat side to the vehicle body floor, wherein feedback signals of the sensors are transmitted to respective drive parts of the three pantograph links via a control unit configured to individually control the first arms and the second arms of each pantograph link by the drive parts respectively to control the pantograph links corresponding to input vibrations from the vehicle body floor and displace the seat side in six-axis directions. three pantograph links disposed at equal intervals in a circumferential direction in plan view, wherein the pantograph links have first arms and second arms on the left and the right, and when facing the first arms and the second arms, the left arms substantially form the shape of a less-than sign, and the right arms substantially form the shape of a greater-than sign, sensors configured to detect a relative posture of the seat side to the vehicle body floor, wherein feedback signals of the sensors are transmitted to respective drive parts of the three pantograph links via a control unit configured to individually control the first arms and the second arms of each pantograph link by the drive parts respectively to control the pantograph links corresponding to input vibrations from the vehicle body floor and displace the seat side in six-axis directions.