An intermittent pulse generator 1 is provided between terminals Ti1 and Ti2. In the intermittent pulse generator 1, pulses are generated from an AC power source which is supplied and the generated pulses are supplied to a controller 3. The controller 3 controls a switching circuit 2 in accordance with the pulses from the intermittent pulse generator 1 and a signal from a supplying mode detecting circuit 9. A rectifying circuit constructed by a diode bridge 5 and a capacitor 6 is provided for the secondary side of a transformer 4. An output of the rectifying circuit is supplied to an energy saving mode detecting circuit 7 and a supplying mode detecting circuit 9. The energy saving mode detecting circuit 7 is connected to an output terminal To through a switching circuit 8. When the energy saving mode is detected in the energy saving mode detecting circuit 7, a signal is supplied to the intermittent pulse generator 1.