A charge/discharge system comprising: a motor generator adapted to serve as a driving power source for driving a vehicle and perform electric power generation using power of a vehicle; an engine adapted to serve as another driving power source for driving the vehicle, wherein the motor generator is adapted to generate electric power using a driving force of the engine; a capacitor adapted to supply electric power to the motor generator and charge electric power generated by the motor generator; a battery; an electric power converter adapted to complementarily perform charging/ discharging between the capacitor and the battery wherein the battery is connected to the capacitor via the electric power converter; electric accessories adapted to be driven by the electric power from the battery; and a controller (50, 100) adapted to control operations of the motor generator, the engine, and the electric power converter, wherein the controller (50, 100) is adapted to drive the vehicle using driving power from at least one of the motor generator and the engine; and wherein the controller (50, 100) is adapted to control the electric power converter such that electric power generated by the motor generator is charged in the capacitor when a state-of-charge of the capacitor is lower than a first predetermined value, and electric power charged in the capacitor is charged in the battery when a state-of-charge of the battery is lower than a second predetermined value, wherein the second predetermined value is set to a value where the battery can stably supply electric power to the electric accessories; characterized in that the controller is adapted to, if the state-of-charge of the capacitor becomes lower than a predetermined threshold, and when both the driving force of the engine and the driving force of the motor generator are used in the travelling, control the electric power converter to perform charging from the battery to the capacitor, so that electric power charged in the battery as well as the capacitor can be used as electric power supplied to the motor generator during travel of the vehicle. a motor generator adapted to serve as a driving power source for driving a vehicle and perform electric power generation using power of a vehicle; an engine adapted to serve as another driving power source for driving the vehicle, wherein the motor generator is adapted to generate electric power using a driving force of the engine; a capacitor adapted to supply electric power to the motor generator and charge electric power generated by the motor generator; a battery; an electric power converter adapted to complementarily perform charging/ discharging between the capacitor and the battery wherein the battery is connected to the capacitor via the electric power converter; electric accessories adapted to be driven by the electric power from the battery; and a controller (50, 100) adapted to control operations of the motor generator, the engine, and the electric power converter, wherein the controller (50, 100) is adapted to drive the vehicle using driving power from at least one of the motor generator and the engine; and wherein the controller (50, 100) is adapted to control the electric power converter such that electric power generated by the motor generator is charged in the capacitor when a state-of-charge of the capacitor is lower than a first predetermined value, and electric power charged in the capacitor is charged in the battery when a state-of-charge of the battery is lower than a second predetermined value, wherein the second predetermined value is set to a value where the battery can stably supply electric power to the electric accessories; characterized in that the controller is adapted to, if the state-of-charge of the capacitor becomes lower than a predetermined threshold, and when both the driving force of the engine and the driving force of the motor generator are used in the travelling, control the electric power converter to perform charging from the battery to the capacitor, so that electric power charged in the battery as well as the capacitor can be used as electric power supplied to the motor generator during travel of the vehicle.