To solve the problem of conventional information communication that wiretapping is theoretically possible by taking out a light beam from an optical fiber and wiretapping cannot be prevented even if the light beam passing through an optical fiber is encrypted.

A light beam irradiated from a light source is split into two by a first beam splitter and one light beam is equipped with an optical switch. A signal for controlling that optical switch is a transmission signal. The split light beams are combined by a second beam splitter and detected by first and second detectors. Subsequently, interference is detected respectively and a receiver is operated with the detected signal thus transmitting/receiving information.