There is provided a casing material for a storage cell having sufficient corrosion resistance and strength even under a charging environment of a high voltage exceeding 2.8 V. This casing material for the storage cell comprises C: not more than 0.03 mass %, Si: 0.01-0.50 mass %, Mn: not more than 0.20 mass %, P: not more than 0.04 mass %, S: not more than 0.0010 mass %, Ni: 20.0-40.0 mass %, Cr: 20.0-30.0 mass %, Mo: 5.0-10.0 mass %, Al: 0.001-0.10 mass %, N: 0.10-0.50 mass %, Ca: not more than 0.001 mass %, Mg: 0.0001-0.0050 mass %, 0: not more than 0.005 mass %, provided that contents of Cr, Mo and N satisfy Cr+3.3×Mo+20×N≧43, and the balance being substantially Fe and inevitable impurities, in which a content of CaO as an oxide inclusion in steel is not more than 20 mass %.