Abstract: An electron gun for a color cathode ray tube includes a last accelerating electrode having a large-caliber electron beam passing hole for commonly passing red, blue, and green electron beams. Both ends of the beam passing hole include circular arc portions formed with a predetermined curvature. The center portions where the green electron beam passes through protrude by a predetermined width. The length of the protrusion in the horizontal direction satisfies the following inequality: L<H-2R(1+cos .alpha.), where H designates the horizontal width of the large-caliber electron beam passing hole, R is the radius of the circular arc portions and .alpha. is the angle between a line drawn from either center of the circular arc portions to an adjacent apex of the protrusions and a line connecting centers of both circular arc portions.