To prevent burning of a cathode ray tube by a spot at the time of power on and off by providing a common power source for a feedback circuit and a differential amplifier circuit, performing a spot killer operation by introducing a time difference using a diode and a capacitor at the time of power off, and also providing a control circuit using a mute signal.

When the power source of the device is turned on, a mute voltage input terminal 12 is turned into 'H', and a control transistor 9 is turned on. The base voltage of a transistor 6 for differential amplification with which the collector is connected is decreased so that emitter current may be amplified, and the emitter current of a transistor 7 for differential amplification is decreased. Thus, the base current of a transistor 3 for a G1 voltage output is decreased, and voltage drop due to a resistor 13 is deceased so that a G1 voltage may be decreased. After a certain time when a power source circuit is made stable, a mute signal is turned into 'L', and a G1 voltage control circuit is turned into a normal operation.