An electric power supply system includes a connecting device that connects a secondary battery provided in a vehicle to a building, and a control apparatus that i) identifies the type of the vehicle that is connected to the connecting device, the type of the secondary battery, or the type of electric power that is distinguishable by the charging source of the electric power stored in the secondary battery, ii) determines a preset electric power supply method based on the identification results, and iii) controls a supply of electric power from the secondary battery to the building based on the determined electric power supply method.