An occupant restraint system includes an occupant restraint device on a side face of an automobile interior, at least one of an acceleration sensor for detecting a lateral acceleration of the automobile and a roll sensor for detecting a roll of the automobile, and a determining unit. A detected signal is input into the determining unit. The determining unit determines a rollover or an overthrow of the automobile based on the detected signals, and calculates a head position of the occupant using the detected signals. Then, the determining unit activates the occupant restraint device, when the rollover is determined to have happened and the calculated head position is determined to be close to the occupant restraint device.