A power supply system (100, 200, 300,400, 500), comprising: a solar cell; a non-isolated type DC/DC converter, boosting a DC voltage from the solar cell input from an input end with a predetermined boosting ratio and outputting a DC voltage from an output end; and an inverter, converting the DC voltage output from an output end of the DC/DC converter into an AC voltage, the power supply system (100, 200, 300, 400, 500,) being connected to an external power system for system interconnection, wherein the power supply system (100, 200, 300, 400, 500,) comprises a potential adjustment device (130, 131, 132, 133, 134, 135, 136, 137, 138) for applying a voltage of an external power system to the solar cell via the inverter to set a ground potential of a negative electrode of the solar cell to positive when an output of the solar cell is smaller than a predetermined value; the power supply system (100, 200, 300, 400, 500) being characterized in further comprising: an AC voltage measurement circuit, measuring an AC voltage at an output end of the inverter connected to the power system, wherein, when the output of the solar cell is smaller than the predetermined value, the voltage of the external power system is applied to the solar cell via the inverter and the AC voltage measurement circuit; and a circuit arrangement in which: the potential adjustment device includes a first resistor, a second resistor, and a diode, one end of the first resistor is connected to a positive electrode on a DC side of the inverter, and the other end of the first resistor is connected to a negative electrode of the inverter and the negative electrode of the solar cell, an anode of the diode is connected to the negative electrode of the inverter, and a cathode of the diode is connected to the negative electrode of the solar cell and one end on a negative electrode side of the first resistor, and one end of the second resistor is connected to the negative electrode of the inverter, the other end of the second resistor is connected to the negative electrode of the solar cell and one end on the negative electrode side of the first resistor, and the second resistor is connected in parallel to the diode. a solar cell; a non-isolated type DC/DC converter, boosting a DC voltage from the solar cell input from an input end with a predetermined boosting ratio and outputting a DC voltage from an output end; and an inverter, converting the DC voltage output from an output end of the DC/DC converter into an AC voltage, the power supply system (100, 200, 300, 400, 500,) being connected to an external power system for system interconnection, wherein the power supply system (100, 200, 300, 400, 500,) comprises a potential adjustment device (130, 131, 132, 133, 134, 135, 136, 137, 138) for applying a voltage of an external power system to the solar cell via the inverter to set a ground potential of a negative electrode of the solar cell to positive when an output of the solar cell is smaller than a predetermined value; the power supply system (100, 200, 300, 400, 500) being characterized in further comprising: an AC voltage measurement circuit, measuring an AC voltage at an output end of the inverter connected to the power system, wherein, when the output of the solar cell is smaller than the predetermined value, the voltage of the external power system is applied to the solar cell via the inverter and the AC voltage measurement circuit; and a circuit arrangement in which: an AC voltage measurement circuit, measuring an AC voltage at an output end of the inverter connected to the power system, wherein, when the output of the solar cell is smaller than the predetermined value, the voltage of the external power system is applied to the solar cell via the inverter and the AC voltage measurement circuit; and a circuit arrangement in which: the potential adjustment device includes a first resistor, a second resistor, and a diode, one end of the first resistor is connected to a positive electrode on a DC side of the inverter, and the other end of the first resistor is connected to a negative electrode of the inverter and the negative electrode of the solar cell, an anode of the diode is connected to the negative electrode of the inverter, and a cathode of the diode is connected to the negative electrode of the solar cell and one end on a negative electrode side of the first resistor, and one end of the second resistor is connected to the negative electrode of the inverter, the other end of the second resistor is connected to the negative electrode of the solar cell and one end on the negative electrode side of the first resistor, and the second resistor is connected in parallel to the diode.