A best-cell amendment method is disclosed for amending hysteresis margins according to the degree of congestion. A radio network controller (RNC) compares the average value P(k) of transmission power of a downlink shared channel PDSCH of cell k and a first threshold value P_threshold1 to measure the degree of congestion. If the RNC determines that the degree of congestion in cell k is high, it sets a small hysteresis margin hm_a, and if RNC determines that the degree of congestion in cell k is low, it sets a large hysteresis margin hm_b.