The present invention proposes a method for transmitting data considering a non-contact state of a human body, while selecting a central frequency in various ranges in the human body communication system. To this end, a first embodiment of the present invention proposes a human body communication system in which a central frequency can be simply moved, and specifically, proposes a data transmission apparatus comprising a frequency shifter which shifts the output of a multiplexer into a specified frequency so as to enable the central frequency to be moved. In addition, a second embodiment of the present invention proposes a human body communication system which controls not only central frequency selection and transmission band minimization, but also a data rate, modulation, etc, and thus can perform stable communication in a non-contact state of a human body. Through this, it is possible to maximize the band efficiency, and to transmit data considering a non-contact state of a human body.