Disclosed is a rear-seat occupant protection apparatus, which is designed to protect, during a frontal collision of a vehicle, a rear-seat occupant (B) seated in a rear seat (5) located behind a front seat (3) equipped with a seat belt (7) having a load limiter function. The rear-seat occupant protection apparatus comprises a collision detection device (25) adapted to detect the frontal collision of the vehicle, and a seat-back displacing mechanism adapted, when the frontal collision of the vehicle is detected by the collision detection device, to permit a seat back (12) of the front seat (3) to be displaced frontwardly at a given timing consecutive with a frontward displacement of a front-seat occupant (A) seated in the front seat (3). The rear-seat occupant protection apparatus of the present invention can adequately protect a head of the rear-seat occupant during the frontal collision of the vehicle.