PURPOSE: To measure the film thickness of a liquid crystal anchoring layer handily and at a low cost by utilizing the relationship between rotatory power obtained, by measurement and the thickness of liquid crystal and rotatory power of liquid crystal.
CONSTITUTION: The height l of spacers 4a and 4b is set in plurality l 1 Wl 5 and a plurality of liquid crystal cells having gaps according to respective heights are prepared. Then, normal light is projected into respective liquid crystal cells and a rotatory power meter is used to measure the rotatory power from the incident light L 1 and emission light L 2 . As a result, the relationship between the cell gaps 4l 1 Wl 5 and the rotatory power is obtained. The relationship is expressed in the X-Y coordinates (X axis: cell gap and Y axis: rotatory power). Then the cell gap is read out at a point where a straight light connecting dots intersects the X axis, namely, a point where the rotatory power is zero. This value gives the thickness of the anchoring layer.