A light modulator includes a light guide to guide light by total internal reflection, a diffraction grating at a surface of the light guide, and a liquid crystal in contact with the diffraction grating. A node can receive two or more RTS packets and identify the RTS packet corresponding to its own cell, as well as RTS packets belonging to interferers. In a case where a front approaching body recognition unit judges that a material body approaches from in front of the own vehicle, and when the frequency judgment unit judges that a frequency component not lower than the frequency threshold exists, it is judged that the material body is a stationary body and is not a warning object. After cleavage, the antigens contribute to the immune response in a separate manner. Thus, the recorded stream can be handled program by program in a later editing or playback operation, despite that it was recorded by booked recording for which only the time zone was specified, and thus the user-friendliness is improved.