Abstract: A Fe—Ni—Co alloy having improved proof stress and Youngs modulus while retaining low thermal expansivity for press-formed fully flat mask, comprising 30-35% Ni, 2-8% Co, 0.01-0.5% Mn, a total of 0.01-0.8% of one or two or more elements selected from the group consisting of 0.01-0.8% each of Nb, Ta, and Hf, and the balance Fe and unavoidable impurities. The impurities are preferably limited to the ranges of C: ≦0.01%, Si: ≦0.04%, P: ≦0.01%, S: ≦0.01%, and N: ≦0.005%. The alloy is characterized by a Youngs modulus of no less than 120,000 N/mm2 after annealing at 900° C. for 30 minutes and by a 0.2% proof stress of no less than 300 N/mm2 after annealing at 900° C. for 30 minutes. The invention also provides a press-formed fully flat mask characterized by the use of the Fe—Ni—Co alloy set forth above, and a color picture tube using the fully flat mask of the Fe—Ni—Co alloy.