Seat system for a vehicle

A seat for a passenger (3) comprises reinforcing structure bodies (9,29) reinforcing seatbacks (6,7), connection support portions (14,42) connecting the reinforcing structure bodies (9,29) to a vehicle-body wall portion (4) so as to support the reinforcing structure bodies (9,29) at the vehicle-body wall portion (4), pressure-receiving portions (10,30) provided in the seatbacks (6,7) and supported so as to move rearwardly by being pressed by passengers in a vehicle rear collision, the pressure-receiving portions (10,30) being arranged at a specified height position which is a distance (X) upwardly away from lower end portions of the seatbacks (6,7), and headrest moving-mechanism portions (11,31) moving headrests (6a,7a) forwardly or upwardly in accordance with a rearward move of the pressure-receiving portions (10,30). Accordingly, a passenger's head portion can be protected effectively with a simple structure.