PURPOSE: To effectively prevent contact between eletron beam and internal surface of cone area by providing a thin part having an increasing internal diameter to the funnel part corresponding to the diagonal corners and by extending said thin part viewed from the direction of tube axis, along the diagonal line from the center axis of nearest electron gun to the thin part considered as the origin.

CONSTITUTION: Total of four grooves 12 indicated by the hatched areas are provided on the internal surface 6 of cone area of funnel part corresponding to the diagonal corner part of the panel. These grooves 12 form the thin part with the groove and the internal diameter of funnel of this part is locally increased. When viewed from the phosphor screen side, the groove 12 is so formed that for example, the right side groove 12a is extended radially along the diagonal lines including the axis which connects the diagonal effective diameter points 11 determined from a rectangular having the sides of horizontal and vertical effective diameters with the center axis of the electron gun nearest to the groove 12, namely of the right side electron gun 8a considered as the origin. Therefore, if the electron beam is deflected, for example, to the upper right diagonal corner, the groove is extending in almost the same angle as the locus of electron beam which shows the smallest interval to the internal surface 6.