A coating formed on a surface of a base material, the coating composition containing an ionic polymer (a), a hygroscopic agent (b) and a solvent, the hygroscopic agent (b) being a granular crosslinked product of a monovalent metal salt of a poly(meth)acrylic acid and being contained in an amount of 75 to 700 parts by mass per 100 parts by mass of the ionic polymer (a), and the coating having a haze of 5% or less and a maximum surface roughness Ra (JIS B-0601-1994) of 0.1 μm or less.