An occupant restraint system includes a rollover prediction unit, a
rollover detection unit, primary and secondary pre-tensioner units, and a
control unit. The rollover prediction unit is configured to predict a
rollover of the vehicle based on a state of the vehicle. The rollover
detection unit is configured to detect a rollover of the vehicle based on
the state of the vehicle. The primary and secondary pre-tensioner units
are configured to apply a tension to a seat belt so as to restrain an
occupant in a seat. An operation force of the secondary pre-tensioner
unit is stronger than that of the primary pre-tensioner unit. The control
unit is configured to activate the primary pre-tensioner unit based on a
prediction by the rollover prediction unit that a rollover occurs and
activate the secondary pre-tensioner unit based on a detection by the
rollover detection unit that the rollover occurs.