In order to improve vibration absorbency and impact absorbency, the seat structure includes a swing member provided in a manner to be able to swing at least back and forth on a rear frame member positioned around the rear of a seat cushion, a pelvis supporting member connected to the swing member at the vicinity of the lower portion of the pelvis supporting member and disposed behind the pelvis of a seated person, and coil springs as an elastic member to support the pelvis supporting member biasing in the direction pushing forwards in a normal seating state. Accordingly, vibration inputted from the seat back side and as if patting on the back of the human body can be absorbed by the pelvis supporting member supported elastically. Besides, since the pelvis supporting member is connected to the rear frame member via the swing member, since pivoting movement in the back-and-forth direction of the pelvis supporting member is performed with a connecting portion of the swing member and the rear frame member as the center, and the radius of gyration is large, the vicinity of the lower portion of the pelvis supporting member never presses the pelvis.