Provided are a frequency modulation/demodulation apparatus using a frequency selective baseband and a transmitting/receiving apparatus using the same. In a frequency selective baseband transmission technique or an FS-CDMA technique, a transmission rate is controlled according to communication channel environment, spread code groups are repeatedly selected in a receiving side so as to obtain a frequency diversity gain. Accordingly, it is possible to reduce interference between users. In addition, even in a case where strong interference induced from electronic exists, it is possible to implement low-power, stable human-body communication and to ensure a communication quality.