Abstract: A cathode ray tube control apparatus includes phosphor display screen, three electron guns for emitting R, G, B electron beams to the display screen, a shadow mask placed between the electron guns and the display screen, and index phosphors deposited on the shadow mask and having at least two line elements diagonal to a horizontal scanning direction of the electron beam for generating a signal according to the electron beam scan. Further provided are detector for detecting beam crossing points over the index phosphor, and correction circuit for correcting the deflection of the electron beam based on the detected beam crossing points.