An electric power supply system is provided. The electric power supply system includes charge and discharge devices capable of performing a system interconnection to charge and discharge a power system. At least one of the charge and discharge devices is capable of performing a simulated system operation of supplying electric power of constant power and constant frequency to the power system when an abnormality occurs in a commercial power supply. According to a check result on a state of charge of an electricity storage, electric power supplied from a distributed power supply, and consumption power in a load, the electric power supply system can simultaneously charge or discharge electricity storages of the charge and discharge devices, and preferentially charges the electricity storage of the charge and discharge device performing the simulated system operation, and preferentially discharges the electricity storage of the charge and discharge device performing the system interconnection.