A manual cut-off system makes it possible to manually change operability of each of a plurality of passive safety devices, including air bags. The system aims at accurately maintaining operability of each of the passive safety devices until the air bags are required to operate. If a multistage switch for changing operability of each of the passive safety devices, including air bags, assumes a position for preventing operation of predetermined ones of the passive safety devices, ignition signals are prevented from being outputted to squibs corresponding to those predetermined passive safety devices. A CPU detects a state of the multistage switch based on the voltage between a common contact and a connecting portion of resistors. The thus-detected state of the multistage switch is stored in an IC memory.