To decrease any stress receiving mechanical parts of a drive unit of this restrainer by separating a first chamber and a second chamber from each other by a partition being broken down in time of the burning of first ammunition, and making a housing install a single opening for the gas to be produced by both first and second ammunition.

A first chamber 42 is partitioned off in the inner part of a housing 12, and first ammunition 16' is housed in this first chamber 42. Likewise, a second chamber 44 is partitioned off in the inner part of this housing 12, and second ammunition 16" is housed in this second chamber 44. In addition, the first ammunition 16' is made into a lower turning velocity than that of the second ammunition 16", and they are separated from each other by a consumable partition 28 being broken down in time of the burning of the first ammunition 16'. Moreover, the housing 12 is equipped with a single opening 56 for the gas to be produced by both these first and second ammunition 16' and 16".