In a transmission method, a service area covered by a first cell is provided with a plurality of second cells with a smaller radius than the first cell. A first radio base station belongs to a first cell while the second radio base stations belong to different second cells. A transmitter of the first radio base station transmits a synchronization channel in a given band while a transmitter of each second radio base station transmits a synchronization channel in a band that is different from the given band and also from those of other second radio base stations. A control unit of a mobile station narrows down bands to be observed for detecting synchronization channels to the given band or, if there are some of the second cells that the mobile stations are allowed to access, to the given band and the bands corresponding to the accessible second cells.