The shadow mask of a color cathode ray tube has a number of apertures in the effective area passed by electron beams to the phosphor screen formed in the inner surface of the panel. The effective area where these apertures are distributed is in the nonspherical configuration adjacent to the phosphor screen surface. When taking the major axis as the X axis, the minor axis as the Y axis and the center of the shadow mask through where the tube axis (the Z axis) passes is made as a point of origin, the line of intersection defined by the plane containing the X axis and Z axis (X-Z plane) and the effective area is formed by the curve positioned as the panel side other than three points of which the circular arc passes in common through both terminal points and the center point on the above line of intersection, against the circular arc.