While the concept of “common carrier” has been frequently used as a sort of magic word in order to delineate the purview of constitutional norms, or protection range of freedom of expression through transmission, this usage is not appropriate. This is partly because it is quite unclear who should be regarded as common carriers. In addition, being labeled as common carriers has a virtual effect to eliminate the opportunity to exercise freedom of expression through transmission. Communications service providers engaged in transmission of information have limited range of exercising freedom of expression, while being exempted from responsibilities of content of the information, because the transmission directly influences on the performance of communications and those providers are bound by constitutional requirements of secrecy of communications in offering communications services. On the other hand, communications service providers who are not involved in transmission essentially have wider range of exercising such freedom, even though they are still bound by the requirements of secrecy of communications. Therefore, it is critical to find whether communications service providers are directly engaged in transmission of information on the network or not in terms of judging the leeway of exercising their own freedom of expression.