A method to compress an unoptimized Aho-Corasick automaton is provided that can be used in network intrusion detection systems. The RFID network transfers ultra-wide band signals between a reader and a tag. In the M-dimensional LUT, record image data optimal under plural observing light sources have been stored corresponding to the image data converted into the vector coefficients. In the case of recording conducted on the disk medium by a laser beam, a transmission factor of the diffraction optical element is made higher than the diffraction efficiency in the case of reading and a transmission factor of the diffraction optical element is made lower than the diffraction efficiency in the case of recording.