Electrodes of an electron gun including a pair of first and second outer rim electrode members installed to face one another and where large diameter electron beam apertures through which three electron beams pass are respectively formed, and first and second inner electrode member installed in the outer rim electrode members, respectively, and where three small diameter electron beam apertures are formed to have an in-line shape. In the above electrodes, a burring portion is formed at the edge of the large diameter electron beam aperture of the first outer rim electrode member at one side of the outer rim electrode members facing each other, and the vertical diameter of the electron beam aperture formed in the middle of the small diameter electron beam apertures formed at the first inner electrode is formed to be greater than those of the two other small diameter electron beam apertures.