A redundant power supply system that includes: a first power supply system (1A, 201A) and a second power supply system (1B, 201B) connected in parallel and connectable to a power supply unit, the first power supply system (1A, 201A) including a first power supply and a first system to which power is supplied from the first power supply, the second power supply system (1B, 201B) including a second power supply and a second system to which power is supplied from the second power supply, and a power supply control system comprising: a first switch (11, 211) that is a MOSFET provided between the power supply unit and the first power supply; a second switch (12, 212) that is a MOSFET provided between the power supply unit and the second power supply; a first wiring configured to supply a dark current flowing from the first power supply to the second system; a first relay (14, 114) of a normally-on type provided on the first wiring; and a second relay of a normally-off type provided on a second wiring connecting the second power supply system (1B, 201B) and the second power supply; characterized by the power supply control system comprising: a third switch (13, 213) that is a MOSFET, the third switch (13, 213) being provided between the first switch (11,211) and the power supply unit and between the second switch (12, 212) and the power supply unit, the third switch (13, 213) being configured to cut off a current flowing from a side of the power supply unit to both a side of the first power supply system (1A, 201A) and a side of the second power supply system (1B, 201B) in an off state of the third switch (13, 213); wherein the first switch (11,211) is configured to cut off a current flowing from a side of the first power supply system (1A, 201A) to a side of the power supply unit in an off state of the first switch (11, 211); and wherein the second switch (12, 212) is configured to cut off a current flowing from a side of the second power supply system (1B, 201B) to a side of the power supply unit in an off state of the second switch (12, 212). a first power supply system (1A, 201A) and a second power supply system (1B, 201B) connected in parallel and connectable to a power supply unit, the first power supply system (1A, 201A) including a first power supply and a first system to which power is supplied from the first power supply, the second power supply system (1B, 201B) including a second power supply and a second system to which power is supplied from the second power supply, and a power supply control system comprising: a first switch (11, 211) that is a MOSFET provided between the power supply unit and the first power supply; a second switch (12, 212) that is a MOSFET provided between the power supply unit and the second power supply; a first wiring configured to supply a dark current flowing from the first power supply to the second system; a first relay (14, 114) of a normally-on type provided on the first wiring; and a second relay of a normally-off type provided on a second wiring connecting the second power supply system (1B, 201B) and the second power supply; a first switch (11, 211) that is a MOSFET provided between the power supply unit and the first power supply; a second switch (12, 212) that is a MOSFET provided between the power supply unit and the second power supply; a first wiring configured to supply a dark current flowing from the first power supply to the second system; a first relay (14, 114) of a normally-on type provided on the first wiring; and a second relay of a normally-off type provided on a second wiring connecting the second power supply system (1B, 201B) and the second power supply; characterized by the power supply control system comprising: a third switch (13, 213) that is a MOSFET, the third switch (13, 213) being provided between the first switch (11,211) and the power supply unit and between the second switch (12, 212) and the power supply unit, the third switch (13, 213) being configured to cut off a current flowing from a side of the power supply unit to both a side of the first power supply system (1A, 201A) and a side of the second power supply system (1B, 201B) in an off state of the third switch (13, 213); wherein the first switch (11,211) is configured to cut off a current flowing from a side of the first power supply system (1A, 201A) to a side of the power supply unit in an off state of the first switch (11, 211); and wherein the second switch (12, 212) is configured to cut off a current flowing from a side of the second power supply system (1B, 201B) to a side of the power supply unit in an off state of the second switch (12, 212).