An auxiliary power supply system (6, 14, 16, 30) for electric vehicle comprising: an inverter configured to convert DC power input from an overhead wire into AC power, a motor configured to drives wheels of the electric vehicle using the AC power supplied by the inverter, a circuit breaker is configured to be placed between the DC power side of the inverter and the overhead wire, to cut electrical conduction between the overhead wire and the inverter or to make electrical conduction between the overhead wire and the inverter, an electricity storage configured to store electric power supplied from the overhead wire supplying the electric power to the inverter, the electricity storage being connected in parallel to the overhead wire with respect to the inverter, the electricity storage being connected through a voltage boosting circuit (32, 35) connected in parallel to the overhead wire with respect to the inverter, the voltage boosting circuit (32, 35) configured to boost a voltage supplied from the electricity storage and provide the boosted voltage to the inverter,; a diode configured to allow a current to flow in one direction,; a current sensor configured to detect the current flowing through the diode; and a controller configured to perform a predetermined control when the current is detected by the current sensor, characterized in that the diode being placed in series with the electricity storage between the electricity storage and the voltage boosting circuit, the one direction being direction from the electricity storage to the DC power side of the inverter, a first side of the diode being connected to the electricity storage, a second side of the diode being connected to between the DC power side of the inverter and the circuit breaker, wherein the controller, when the current is detected by the current sensor, is configured to cause the circuit breaker to cut electrical conduction between the overhead wire and the inverter, to cause the voltage boosting circuit (32, 35) to boost a voltage supplied from the electricity storage, and to provide the boosted voltage to the inverter as a predetermined control. an inverter configured to convert DC power input from an overhead wire into AC power, a motor configured to drives wheels of the electric vehicle using the AC power supplied by the inverter, a circuit breaker is configured to be placed between the DC power side of the inverter and the overhead wire, to cut electrical conduction between the overhead wire and the inverter or to make electrical conduction between the overhead wire and the inverter, an electricity storage configured to store electric power supplied from the overhead wire supplying the electric power to the inverter, the electricity storage being connected in parallel to the overhead wire with respect to the inverter, the electricity storage being connected through a voltage boosting circuit (32, 35) connected in parallel to the overhead wire with respect to the inverter, the voltage boosting circuit (32, 35) configured to boost a voltage supplied from the electricity storage and provide the boosted voltage to the inverter,; a diode configured to allow a current to flow in one direction,; a current sensor configured to detect the current flowing through the diode; and a controller configured to perform a predetermined control when the current is detected by the current sensor, characterized in that the diode being placed in series with the electricity storage between the electricity storage and the voltage boosting circuit, the one direction being direction from the electricity storage to the DC power side of the inverter, a first side of the diode being connected to the electricity storage, a second side of the diode being connected to between the DC power side of the inverter and the circuit breaker, wherein the controller, when the current is detected by the current sensor, is configured to cause the circuit breaker to cut electrical conduction between the overhead wire and the inverter, to cause the voltage boosting circuit (32, 35) to boost a voltage supplied from the electricity storage, and to provide the boosted voltage to the inverter as a predetermined control.