The present invention relates to an ignition device for an idle stop & go system (ISG)-equipped vehicle using a liquefied petroleum gas (LPG) as a fuel. According to the present invention, an auxiliary LPG switch is separately installed. Said auxiliary LPG switch can sense the ON/OFF state of the LPG switch, drive a plurality of fuel cut-off solenoid valves, and be switched on/off together with the LPG switch. Therefore, the ON/OFF state of said LPG switch can be determined according to the second output voltage of the auxiliary LPG switch, and then ISG control can be implemented. After the fuel cut-off solenoid valves are driven by the relay's second voltage output by the auxiliary LPG switch, the fuel pressure in the fuel pipeline remains in the state before the idle stop to improve the starting performance of the engine at the time of restarting. In addition, in the case of an emergency, the LPG SW and the auxiliary LPG SW are simultaneously switched off, the fuel cut-off solenoid valves are quickly switched off and the fuel pump motor is also stopped so that the fuel supply can be cut off quickly and a secondary accident can be prevented in advance.