Inline electron gun and color cathode ray tube

An inline electron gun that emits three electron beams aligned along a horizontal direction, comprising

• a cylindrical low potential side electrode provided with a first flat plate electrode;
• and
• a cylindrical high potential side electrode provided with a second flat plate electrode, where the low potential side electrode and the high potential side electrode are arranged in the stated order along a direction in which the electron beams are headed so as to make up a main electrostatic lens,
• wherein
• each of the first flat plate electrode and the second flat plate electrode has a central passage hole for letting a central electron beam of the three electron beams pass therethrough and two outer passage holes for letting each of the other two outer electron beams pass therethrough,
• each of opening geometries of the two outer passage holes in the first flat plate electrode and each of opening geometries of the two outer passage holes in the second flat plate electrode are configured with a higher-order curve,
• each of the opening geometries of the two outer passage holes in at least one of the first flat plate electrode and the second flat plate electrode is formed by combining two higher-order curves having different degrees with a boundary on a center line of the outer passage hole along a vertical direction, and an opening geometry of one outer passage hole and an opening geometry of the other outer passage hole provided in a same flat plate electrode are symmetric with respect to a center line of a central passage hole provided in the same flat plate electrode along the vertical direction, and
• in a higher-order curve forming the opening geometries of the outer passage holes provided in the first flat plate electrode, at least one of (a) inner portions of the higher-order curve located at the side of the central passage hole with respect to the center lines of the respective outer passage holes along the vertical direction and (b) outer portions of the higher-order curve located outside have a different degree from a degree of corresponding portions of a higher-order curve forming the opening geometries of the outer passage holes provided in the second flat plate electrode.