Black and white picture tubes, with the exception of certain special purpose tubes, are currently all nearly wide-angle deflection types. Similarly, wide deflection angles are now being adopted in the color picture tube field. Since the principle of the color picture tube is far more complex than that of the black and white tube, a sophisticated production technology is necessary, and consequently production techniques of wide deflection angle color tubes are less advanced at present. Companies producing the conventional 3-gun shadow mask tube recently have successively announced improvement of their mass production technology and have greatly changed the design of the tube itself in their efforts to achieve ease of production comparable to that of the 90°deflection tube. Since their principal objective is to make the picture tube thinner, achievement of picture quality at the same level as in the 90°deflection tube is one of the problems.