Provided is an automatic brightness stabilization (ABS) apparatus that prevents brightness stabilization from being affected by dynamic focus device and velocity modulation device. ABS apparatus includes an image signal processing portion which inserts a predetermined pulse signal into a vertical flyback period of an image signal and applies the resulting signal to the electron gun, an ABS signal detecting portion which detects the pulse signal affected by the electron gun, a velocity modulating portion which generates a velocity modulation signal for emphasizing luminance components of the image signal and applies the velocity modulation signal to a velocity modulation coil of the CRT, and a retrace cancelling portion which cancels the velocity modulation signal generated by the velocity modulating portion, during a vertical flyback period. Image signal processing portion compares the detected pulse signal with a predetermined amplitude of the pulse signal and controls the amplification degree of the image signal.