Disclosed is a process which can be used on an industrial scale for preparing and purifying 1,7-dimethyl-2-propyl-2,5-bi-1H-benzimidazole in which the crude product is subjected to charcoal treatment. The electrooptical deflector includes a material that has a different refractive index for different polarization states and changes its refractive index in response to voltage. Then, the substrate and the compound semiconductor film are separated from each other by irradiation of laser light, polishing of the substrate, etching, cutting, etc. The DCT coefficients are transformed into an intermediate exchange format. The apex of the one-end side bent portion of each wavy annular member and the apex of the other-end side bent portion of the adjacent wavy annular member curve in an approach direction, thus engaging each other.