An electron gun for emitting an electron beam to a phosphor screen and for scanning one of two scanning regions defined in the phosphor screen is arranged in two necks of a vacuum envelope. A mask body of a shadow mask has two effective areas, in which numerous electron beam passage apertures are bored, defined in association with the scanning regions, and has a boundary portion defined between the effective areas and opposed to the boundary between the scanning regions of the phosphor screen. An adjustment member used to adjust a q value at a plurality of points on the boundary portion is fixed to the inner surface of the boundary portion. After the q value is adjusted, the adjustment member is fixed to the mask frame.