To manufacture a retardation film in which Re(retardation in a surface direction) is 30 nm and Rth(retardation in a thickness direction) is 100 nm.

Both side end parts of a polymer film are held by a clip 65a and is broadened by 1.2 to 1.7 times. During broadening the film 62 is heated so that temperature of the film 62 is held in a range between (Tg-10) and (Tg+80). Further broadened polymer film 62 is heated in a heating chamber 69. Heating condition is chosen from among (1)Tg-20TTg-15, 50F150, 240t360, (2)Tg-15TTg-10, 50F100, 180t300, (3)Tg-10TTg-5, 50F70, 30t150, wherein T denotes temperature (C) of the film 62, F denotes conveyance tension (N/m), t denotes temperature holding time (second) and conveyance tension F is a value per 1m of the film 62 in a width direction.