An electric power supply system comprising: a first power converter which is connected to a first power generator configured to generate electric power that is allowed to flow back to a power grid and which is configured to carry out electric conversion of generated power of the first power generator; a second power converter which is connected to a storage battery and which is configured to charge and discharge the storage battery; and a third power converter which is connected to a second power generator configured to generate electric power that is forbidden to flow back to the power grid and which is configured to carry out electric conversion of generated power of the second power generator, wherein the electric power supply system is configured to supply electric power to at least one load through a grid-connected feed line, said power grid being connected to an upstream end of the grid-connected feed line, said load being connected to a downstream end of the grid-connected feed line, the first to third power converters (3, 5, 7) are connected to the grid-connected feed line in a manner that the first power converter is located at most upstream side of the grid-connected feed line, the electric power supply system further comprises a first sensor which is disposed at a position between a junction of the grid-connected feed line and the first power converter and a junction of the grid-connected feed line and one of the second and third power converters (5, 7), located at more upstream side of the grid-connected feed line, said first sensor being configured to sense electric power flowing back to the power grid through the grid-connected feed line, and the second power converter is configured to control charging and discharging of the storage battery so that the electric power flowing back to the power grid, sensed with the first sensor is kept zero, and the third power converter is configured to control output power thereof to the grid-connected feed line so that the electric power flowing back to the power grid, sensed with the first sensor is kept zero, wherein said one of the second and third power converters (5, 7), located at more upstream side of the grid-connected feed line is connected to the first sensor, the second and third power converters (5, 7) are configured to control the charging and discharging of the storage battery and to control the output power of the third power converter to the grid-connected feed line while communicating with each other so that the electric power flowing back to the power grid, sensed with the first sensor is kept zero. a first power converter which is connected to a first power generator configured to generate electric power that is allowed to flow back to a power grid and which is configured to carry out electric conversion of generated power of the first power generator; a second power converter which is connected to a storage battery and which is configured to charge and discharge the storage battery; and a third power converter which is connected to a second power generator configured to generate electric power that is forbidden to flow back to the power grid and which is configured to carry out electric conversion of generated power of the second power generator, wherein the electric power supply system is configured to supply electric power to at least one load through a grid-connected feed line, said power grid being connected to an upstream end of the grid-connected feed line, said load being connected to a downstream end of the grid-connected feed line, the first to third power converters (3, 5, 7) are connected to the grid-connected feed line in a manner that the first power converter is located at most upstream side of the grid-connected feed line, the electric power supply system further comprises a first sensor which is disposed at a position between a junction of the grid-connected feed line and the first power converter and a junction of the grid-connected feed line and one of the second and third power converters (5, 7), located at more upstream side of the grid-connected feed line, said first sensor being configured to sense electric power flowing back to the power grid through the grid-connected feed line, and the second power converter is configured to control charging and discharging of the storage battery so that the electric power flowing back to the power grid, sensed with the first sensor is kept zero, and the third power converter is configured to control output power thereof to the grid-connected feed line so that the electric power flowing back to the power grid, sensed with the first sensor is kept zero, wherein said one of the second and third power converters (5, 7), located at more upstream side of the grid-connected feed line is connected to the first sensor, the second and third power converters (5, 7) are configured to control the charging and discharging of the storage battery and to control the output power of the third power converter to the grid-connected feed line while communicating with each other so that the electric power flowing back to the power grid, sensed with the first sensor is kept zero.