Arm-fire device and method of igniting propulsion system using the same

An arm-fire device comprises a capacitor charged by an arming signal; an acceleration switch for generating an operation signal if an acceleration more than a predetermined acceleration is sensed; a controller electrically connected with the capacitor and the acceleration switch, controlling generation of a firing signal; and a through bulkhead initiator provided with an ignition portion installed at a space separated by a bulkhead and configured to be electrically connected with the controller to ignite the ignition portion if the firing signal is transferred thereto, wherein the controller discharges the capacitor to generate the firing signal when the operation signal and a launching signal, which is applied from outside, are all sensed in a state that the capacitor is charged. The arm-fire device is applied to a multi-stage rocket, etc., whereby the probability of accidental ignition may be lowered.