An object of the present invention is to provide a radio quality estimation system, a base station, a mobile station, and a radio quality estimation method whereby, regardless of influence of fading, a radio quality of a predetermined measurement period is more accurately estimated. An interference power calculator calculates an interference-signal power of each of local estimation intervals which are parts of the predetermined estimation interval. An SIR calculator calculates an SIR of the predetermined estimation interval based on the interference-signal powers calculated by the interference power calculator.