PURPOSE: To concurrently operate another air bag by installing a pressure switch on a gas generator operated by a mechanical sensor, and connecting the pressure switch to the electric percussion cap of the other air bag.

CONSTITUTION: A power source 1 is used to detonate an electric percussion cap 7 for a gas generator 5' for expanding a slave bag 6', and a pressure switch 3 is connected to the electric percussion cap 7 and the power source 1 by lead wires 2. When a shock sensor 4 detects a shock and operates a gas generator 5, the gas generated by the gas generator 5 expands a master bag 6 and generates pressure, the pressure switch 3 is closed, a current flows in the electric percussion cap 7 nearly instantaneously, and a gas generator 5' is operated to expand the slave bag 6'. A multiple-air bag system which has high reliability and can protect multiple crews at a low cost can be constituted.