An apparatus for filling a liquefied petroleum gas (LPG) vehicle with LPG may include an auxiliary chamber disposed in an LPG bombe of the LPG vehicle, an auxiliary injection line branched from a fuelling line extending to the LPG bombe from a fuel inlet port for connection to the auxiliary chamber, a solenoid valve mounted in the auxiliary injection line to selectively allow or block a flow of LPG to the auxiliary chamber, a temperature sensor to detect a temperature in the bombe, and a controller to control the solenoid valve to be opened when the temperature detected by the temperature sensor is equal to or higher than a critical temperature.