Vehicles are connected to respective receptacles of houses and are capable of generating commercial AC power to supply the generated electric power to a power transmission line. The vehicles communicate with a management server via the houses and the power transmission line. The vehicles output to the management server such information items concerning the vehicles as vehicle ID, amount of generated electric power and remaining amount of fuel. When electric power shortage occurs, the management server generates a start command and a power generation command for the vehicles based on the information concerning the vehicles to output the generated commands to the vehicles.