A sub-mm wave source based on Cherenkov resonant radiation of a microbunched electron beam radiating coherently in a dielectric-loaded pipe. An intermediary device between a computing device and a network can be alerted that the computing device has entered an energy saving state with wake on LAN enabled. One of the plate and the cover includes a resin member to fix the electro-optical device to the mounting case and a metal member including a window corresponding to the image display region in the electro-optical device.