This is for measuring plane directional phase differences of the first quarter-wave film (103) and the second quarter-wave film (104) by fixing phase retardation axes of the first quarter-wave film (103) of the second quarter-wave film (104) parallel to each other and rotating the phase retardation axes so that they form 45° or 135° with the absorption axis of the lower polarizer (101) or the upper polarizer (102).