To increase the degree of freedom for the design and the space by constructing at least a part of the logo display part with a light-transmission material and placing the photodetector of the light-receiving device, which receives the light passing through the light-transmission material, on the rear side.

A combined body of a transmission diffusing plate 20 composed of an opalescent planar base stock and a mask 30 is joined and fixed to a box shaped opening part 41. The transmission diffusing plate 20 is provided with a logotype shaped projecting part 21 on its surface. A Hole part 31, to which the projecting part 21 is joined, is formed on the mask 30 composed of a nontransmissive base stock. The surface of the transmission diffusing plate 20 and the mask 30 form a plane when the hole part 31 and the projecting part 21 are joined together. The incident light beam through the projecting part 21 of the transmission diffusing plate 20 is made incident on the photodetector 50. Namely the incident light beam through the projecting part 21 of the transmission diffusing plate 20 passes through the inside of the transmission diffusing plate 20 and reaches the photodetector 50 via a space between the transmission diffusing plate 20 and the photodetector 50. The photodetector 50 receives the diffused lightwhich passes through the transmission diffusing plate 20 and converts it into an electric signal.