An illuminator including an optical transmission mechanism includes a transmission-side electric circuit for forming electric signals modulated in response to information, a light source for emitting intensity-modulated light in response to the electric modulated signals, optical wavelength conversion means including fluorescent material for converting part of the intensity-modulated light into illumination light, photoelectric conversion means for receiving another part of the modulated light and converting this part into reproduced electric modulated signals and a receiving-side electric circuit for reproducing the information from the reproduced electric modulated signals.