Abstract: Disclosed is a power-supplying apparatus for an electron gun in a color display tube (CDT) provided with an fly back transformer (FBT) having a focus voltage output terminal and an acceleration voltage output terminal, further having a power supplying part supplying a predetermined reference voltage; a focus voltage detection part detecting a focus voltage of the focus voltage output terminal; and a focus voltage boost part boosting the focus voltage of the focus voltage output terminal in case that the focus voltage detected by the focus voltage detection part is lower than the reference voltage of the power supplying part. With this configuration, it is possible to recover the voltage of the focus voltage output terminal dropped according to the grid discharging of the electron gun in the color display tube to the normal voltage.