A high-voltage system control device is used for a vehicle provided with a high-voltage system including a motor as a power source and a battery to supply electric power to the motor. The device includes: an inter-vehicle distance detection unit to detect an inter-vehicle distance between the vehicle and an target such as a preceding vehicle; an automatic brake to automatically brake the vehicle according to the inter-vehicle distance; and a cut-off control unit to cut off the high-voltage system when the automatic brake is activated. When the vehicle is traveling at a high vehicle speed and the automatic brake is activated, the high-voltage system is cut off with a main relay.