A method for communication between inside and outside of a transmission medium using the transmission medium as a communication line, includes the steps of: receiving an electric signal having information related to a transmission medium from a plurality of sensors inside the transmission medium; conducting the electric signal to the transmission medium; and sensing the electric signal flowing to the outside of the transmission medium. Because a modulating unit is not necessary, a power consumption is minimized. In addition, since an electric signal is directly conducted to a medium, it is not necessary to use an antenna, and thus, degradation of a reception rate according to a directional property of the antenna can be prevented. Moreover, since the electric signal is directly generated in the medium and the medium is directly used as an electric conductor, the overall size of a transmitter is reduced.