A lumbar support mechanism includes a damper having one end supported by the inside of a seat back and the other end capable of extension and contraction. Seesaw links are provided with each having one end connected to the other end and capable of extension and contraction. An intermediate portion is supported at a swing fulcrum by the seat back with the other end extending in the width direction of the seat back, and swung around the swing fulcrum. Pantograph links are connected to the respective seesaw links and are movable up and down in the back and forth direction in conjunction with the swing of the corresponding seesaw links. The lock-release lever is operated to release the lock mechanism of the damper. The extension and contraction force of the damper is transmitted to the pantograph links via the corresponding seesaw links with the pantograph links shifting the pad provided in the seat back.