A base station is configured to transmit a downlink signal to a mobile station located in a sector managed by the base station. The downlink signal is spread using a scrambling code. The base station has a monitor configured to monitor a change of a reception condition of an uplink common channel of the mobile station in the sector, a DOA estimator configured to estimate a direction of arrival of an uplink signal transmitted from the mobile station, in response to the change, an area border setter (3) configured to separate the sector into a plurality of areas, by setting an area border in the sector in accordance with the estimated direction, a scrambling code assigner (2) configured to assign a different scrambling code to each of the separated areas and a spreader configured to spread the downlink signal using the assigned scrambling code in each of the separated areas.