To provide a cellulose derivative excellent in solubility while being an optical film with a small through-thickness retardation (Rth).

The derivative is prepared by substituting some or all of hydroxyl groups of cellulose with an acyl group and a phenylcarbamoyl group, and the film is obtained from cellulose acyl phenylcarbamoyl, wherein the degree of substitution with the phenylcarbamoyl group (DSpc) in an optional total degree of substitution (DStotal) is adjusted so that DStotal>DSpc, and a=0.0550, b=-0.0164, c=-0.0367 and d=-0.0050 are met in the following expression: (a+b×DStotal-d)/(b-c)>DSpc>(a+b×DStotal-e)/(b-c).