A color cathode ray tube has a phosphor screen and an electron gun. The electron gun includes an electron beam generating section for emitting three in-line electron beams toward the phosphor screen and an electron beam focusing section for focusing the electron beams onto the phosphor screen. The electron beam focusing section includes at least one cup-shaped electrode having a tubular portion and a flange formed continuously from the tubular portion. The tubular portion has a generally rectangular cross section having an outwardly curved portion at each side thereof in a direction of arrangement of the three in-line electron beams in a plane perpendicular to the color cathode ray tube axis, the flange has a generally rectangular cross section having an outwardly curved portion at each side thereof in the direction of arrangement of the electron beams in the plane perpendicular to the color cathode ray tube axis, and the flange is formed with a locally thinned-down portion.