A circuit system for a railroad vehicle, the circuit system comprising: a power conversion unit which converts power supplied from an overhead wire into power for driving a motor for running mounted on a railroad vehicle in case where the railroad vehicle is run in a normal mode; a first converter which converts power supplied from the overhead wire into DC power which is lower than a voltage of power supplied to the power conversion unit in the normal mode; a second converter which converts power output from the first converter into power for driving a load mounted on the railroad vehicle; a power storage unit which is electrically connected to an input side of the second converter; a filter capacitor which is provided on a side of power supply from the overhead wire of the power conversion unit; a first charging circuit which charges the filter capacitor using high voltage power supplied from the overhead wire; a second charging circuit which charges the filter capacitor using power supplied from the power storage unit; a discharging circuit which discharges the filter capacitor; and a control unit which inputs regenerative power output from the power conversion unit to the first converter and inputs power having the low voltage output from the first converter to the power storage unit in a case where it is determined that the railroad vehicle is being regenerated at the time of regeneration in the normal mode, wherein the normal mode is a mode for running the railroad vehicle using power supplied from the overhead wire, in a case where the supply of power from the overhead wire is started, the control unit charges the filter capacitor with power supplied from the overhead wire using the first charging circuit, in a case where the normal mode is switched to a self-running mode, the control unit discharges the filter capacitor charged with power supplied from the overhead wire using the discharging circuit and recharges the filter capacitor with power supplied from the power storage unit using the second charging circuit, and the self-running mode is a mode for running the railroad vehicle using power supplied from the power storage unit. a power conversion unit which converts power supplied from an overhead wire into power for driving a motor for running mounted on a railroad vehicle in case where the railroad vehicle is run in a normal mode; a first converter which converts power supplied from the overhead wire into DC power which is lower than a voltage of power supplied to the power conversion unit in the normal mode; a second converter which converts power output from the first converter into power for driving a load mounted on the railroad vehicle; a power storage unit which is electrically connected to an input side of the second converter; a filter capacitor which is provided on a side of power supply from the overhead wire of the power conversion unit; a first charging circuit which charges the filter capacitor using high voltage power supplied from the overhead wire; a second charging circuit which charges the filter capacitor using power supplied from the power storage unit; a discharging circuit which discharges the filter capacitor; and a control unit which inputs regenerative power output from the power conversion unit to the first converter and inputs power having the low voltage output from the first converter to the power storage unit in a case where it is determined that the railroad vehicle is being regenerated at the time of regeneration in the normal mode, wherein the normal mode is a mode for running the railroad vehicle using power supplied from the overhead wire, in a case where the supply of power from the overhead wire is started, the control unit charges the filter capacitor with power supplied from the overhead wire using the first charging circuit, in a case where the normal mode is switched to a self-running mode, the control unit discharges the filter capacitor charged with power supplied from the overhead wire using the discharging circuit and recharges the filter capacitor with power supplied from the power storage unit using the second charging circuit, and the self-running mode is a mode for running the railroad vehicle using power supplied from the power storage unit.