A charge/discharge system is mounted on an electric vehicle using a motor as a driving source, which is driven by electric power charged in a battery, and controls at least one of charge from the outside of the vehicle to the battery and discharge from the battery to the outside of the vehicle. The charge/discharge system comprises a power supply unit for controlling power supply to supply power only to a unit contributing charge/discharge among units connected to a wiring system of driving power for the motor when charge/discharge to/from the battery from/to the outside of the vehicle is performed.