To sufficiently absorb energy of a side frame of a seat cushion at the time of a vehicle rear collision, to sufficiently alleviate the impact.

An impact load of a seated person to be applied on a seat back 14 at the time of a vehicle rear collision, is transmitted to a seat cushion 12 via a connecting part with the seat cushion 12, and impact load energy is absorbed by deforming a cushion side frame 30 of the seat cushion 12. The cushion side frame 30 is formed as a sheet-like frame with a vertically long cross-sectional shape. The plurality of cushion side frames 30 are formed in the seating direction. The plurality of side frames 30A and 30B are connected so as to be bent in the sheet-like direction of the sheet-like frame when the impact load is applied on the seat cushion 12. An energy absorbing means 26 is set for absorbing energy during bending deformation.