Disclosed is a stretched optical compensation film which is a phase difference film containing a cellulose-based resin and having excellent optical properties. The stretched optical compensation film of the present invention contains 0.5 to 30 parts by mass of a β-diketone compound represented by Formula (I) with respect to 100 parts by mass of the cellulose-based resin. Positions R1 and R2 each independently represent an alkyl group having 1 to 20 carbon atoms which is optionally substituted, an arylalkyl group having 7 to 20 carbon atoms which is optionally substituted or an aryl group having 6 to 20 carbon atoms which is optionally substituted. Position R3 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.