an optical sheet; and a polarizing film disposed on said optical sheet; said optical sheet comprising: a retardation film; and a transparent layer provided on one of opposite surfaces of said retardation film; wherein said retardation film exhibits Nz=(nx???nz)/(nx???ny) in a range of from 0.6 to 0.9 and (nx???ny)d in a range of from 200 to 350 nm in which d is a thickness of said retardation film