To reduce whiplash injury of an occupant at the time of rear collision without having an impact on portions other than the head and neck of the occupant.

An occupant crash protection device 1 of a vehicle having a seat belt 31 for restraining the occupant X sitting on a seat 20, and a pretensioner 14 for increasing force for restraining the occupant X by retracting a predetermined amount of the seat belt 31 when predicting collision of an own vehicle W, comprises a rigidity reducing means 16 for reducing rigidity of a backrest face of the occupant X on the seat 20 at the time of operation; a rear collision predicting means 12 for predicting the rear collision of the own vehicle W; and an occupant crash protection means 10 for operating the rigidity reducing means 16 as well as the pretensioner 14 when the rear collision of the own vehicle W is predicted by the rear collision predicting means 12.