PURPOSE: To make constant the interval during which charging current flows through the secondary of a transformer, by varying the primary input voltage of transformer in a charging circuit in proportion to the terminal voltage of a charging capacitor.

CONSTITUTION: A signal is produced from a synchronizing circuit 7 in synchronization with an external synchronization signal in order to switch a switching transistor 3 through a drive circuit 2. The transistor 3 is connected in series with the primary of a transformer 4 so as to charge a capacitor 6 connected through a diode 5 to the secondary. Terminal voltage of the capacitor 6 is inputted to an operational amplifier 10 to control a transistor 9 connected between the transformer 4 and a power source so as to vary the primary input voltage. Consequently, noise is produced only during blanking internal of a horizontal synchronizing signal in a television set.