PURPOSE: To prevent a color phase irregularity, by prescribing the ratio between the vertical and horizontal pitches of the slender through holes of a shadow mask to reduce the drop of the peripheral portion of the mask at the time of formation thereof even if the mask is made of such a material of higher proof stress as Invar than iron.

CONSTITUTION: A shadow mask 11 for a color picture tube is provided with slender through holes 16 which slenderly extend vertically and are disposed at a vertical pitch PV across a bridge 17 and a horizontal pitch PH. The shadow mask 11 is made of such a material of higher proof stress as Invar than iron so that the mask has a low coefficient of thermal expansion. The ratio of the vertical pitch PV to the horizontal pitch PH is set at 0.6W1.3 to prevent the percentage of processing of the shadow mask in the formation thereof from becoming nonuniform. As a result, the drop of the peripheral portion of the shadow mask 11 in forming the mask with a skirt or the like is reduced to prevent a color phase irregularity or the like.