A seat structure which can ameliorate fatigue of a sitting person in accordance with a long period of sitting is provided.In a vehicle seat 10, a back edge side of a lower layer sheet 50 of a cushion material 20, of which a front edge side is fixed to a front edge side of a sitting portion frame 14, is resiliently connected to a back edge side of the sitting portion frame 14 via a movable frame 34 and a torsion bar 46, which is a resilient member. The cushion material 20 has a spring zero characteristic in which a spring constant of a portion that supports a protrusion portion of the sitting person is smaller than a spring constant of other portions. This vehicle seat 10 makes smaller the energy of vibrations which are transmitted to a spinal column portion of the sitting person through the sitting portion frame 14, and peripheral portions thereof convert vibrations corresponding to fluctuations in the body and transmit these through the sitting portion frame 14. α waves of 10 Hz to 12 Hz, which occur in a relaxed waking state, are caused in the brain of the sitting person. Vibrations in a resonance frequency region are attenuated in amplitude and transmitted to the sitting person.