NOVELTY - The system has a vehicular power state detecting element (61a) detecting vehicular power state. A power supply controlling element (62a) switches a plug-out power supply supplying electric power from a vehicular power source i.e. fuel cell (20), to a house (70). A plug-in power supply supplies electric power from a household power source to a vehicle (1a) based on the vehicular power state and a household power state when the vehicular power source and the household power source are connected by a power source connecting element for supplying the electric power in two directions.    USE - Electric power supply system for supplying electric power between a vehicle such as fuel cell vehicle and hybrid electric vehicle, and a house.    ADVANTAGE - The system efficiently supplies the electric power between the vehicle provided with the vehicular power source and the house provided with a household power source in two directions according to the plug-in power supply and the plug-out power supply. The system effectively utilizes the electric power supplied from the vehicular power source in the vehicle and the household power source in the house while appropriately adjusting the temperature of the vehicular power source such as a fuel cell. The connection between the vehicular power source positioned in the vehicle and the household power source positioned in the house for the electric power supply in two directions by the power source connecting element is permitted by the power connection permitting element on condition that the vehicle is not in a position to run, so that the vehicle can be prevented from running by mistake when the vehicle and the house are connected by the power source connecting element.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of an electric power supply system between the fuel cell vehicle and the house.    Vehicle (1a)    Fuel cell (20)    Vehicular power state detecting element (61a)    Power supply controlling element (62a)    House (70)