A seat belt system for a vehicle includes a collision predicting device, an occupant sensing device, a seat belt, a seat belt drive device and a seat belt control device. The collision predicting device senses an imminent collision of the vehicle before the collision actually takes place. The occupant sensing device determines an occupant state on a seat of the vehicle. The seat belt restrains an occupant to the seat. The seat belt drive device retracts and extends the seat belt. The seat belt control device drives the seat belt drive device to retract the seat belt and thereby to achieve a corresponding tension of the seat belt, which corresponds to the occupant, based on a signal outputted from the collision predicting device and occupant information outputted from the occupant sensing device.