To reduce the processing load such as channel assignment and an
authentication process in a plurality of radio base stations and
communication terminals, and quickly and efficiently assign channels to
the communication channels. The channel assigning method by a radio base
station group, includes determining assignment of a communication channel
between a communication terminal entering a radio area of the radio
station group and all radio base stations within the radio station group
by a base station in the radio base station group. Channel assigning
information common to the radio base station group is updated as to the
determined communication channel and a communication channel is assigned
to the communication terminal with reference to the channel assigning
information by each radio base station in the radio base station group
other than the radio base station.