In a radio communication system defining a plurality of bandwidths, mobile terminals of kinds respectively corresponding to the plurality of bandwidths are accommodated in the system, and a minimum transmission bandwidth of the plurality of bandwidths is set as a transmission bandwidth of a downlink common channel. Or, every mobile terminal accommodated in the radio communication system is provided with a capability for processing a bandwidth equal to or greater than a predetermined value, and equal to or more than two transmission bandwidths that are equal to or less than a predetermined value are set as a transmission bandwidth of a downlink common channel. In the latter case, the mobile terminal identifies a bandwidth of a received downlink common channel.