A radio communication system including a radio base station and radio terminals communicating with the radio base station, wherein the system further includes a unit for allocating a first frequency resource which is shared by the radio terminals and which is used when each of the radio terminals transmits a first signal to the radio base station in periodic transmission timing. Also included is a unit for allocating a second frequency resource which is used when each of the radio terminals transmits a second signal to the radio base station. Also included is a unit for controlling the second frequency resource when each of the radio terminals transmits the second signal in transmission timing of the first signal, so that the second frequency resource is changed to a third frequency resource which is smaller than the allocated second frequency resource so as not to overlap the first frequency resource.