Communications apparatus and communications system using multicarrier transmission mode

A base station in a communications system for exchange of information, includes, a transmission data generator configured to generate frequency band information indicating which frequency band is to be used for transmission of data information with a mobile station; a transmitter configured to transmit the frequency band information, using a specific frequency band which is set from among a plurality of frequency band assigned to the communications system, and to transmit data information by using at least one frequency band set from among said plurality of frequency bands; wherein at least one frequency band set from among said plurality of frequency bands, other than the specific frequency band, is made variable, wherein at the time of establishing the wireless channel, the frequency band usable by the mobile station is restricted, at least one frequency band, other than the specific frequency band, are dynamically assigned within that restricted frequency band.