An aluminum-alloy sheet includes 0.10 to 0.40 mass % of Si, 0.35 to 0.80 mass % of Fe, 0.10 to 0.35 mass % of Cu, 0.20 to 0.80 mass % of Mn, and 1.5 to 2.5 mass % of Mg, the balance being Al and unavoidable impurities, wherein a content ratio (Si/Fe) of the Si to the Fe is 0.75 or less, the area fraction of Mg2Si intermetallic compound grains having a maximum length of 1 μm or more is 0.10% or more in a region of a section of the aluminum-alloy sheet, the region being a central region in the thickness direction of the aluminum-alloy sheet, and the aluminum-alloy sheet has a proof stress of 225 to 270 N/mm2 after having been baked at 270° C. for 20 seconds.