To provide a technique for reading identification information written on an index even in observing the identification information from either of a plurality of prescribed viewing points, for example, in observing the information from an oblique direction, and then, for rightly discriminating the read identification information.

The image in a real cavity is obtained, where a plurality of indexes having a lenticular lens for optically changing the observation image of an identifier are arranged so that the observation images become almost the same, even when the identifier is viewed from a plurality of prescribed viewing points and the projected index image is detected in the image (S201), then, the index is discriminated by reading the identifier from the projected image with the detected index (S204).