A mobile communication system using an adaptive multiantenna realizes improvement of reception characteristics, effective use of the band, and optimization of the throughput in comparison with a system in which application of the same multiantenna communication method is continued irrespective of a variation of the number of radio relay stations. The mobile communication system comprises a radio base station, a radio relay station, and mobile terminal stations for communicating with the radio base station through a radio relay station. The radio base station has a multiantenna and is characterized in that the radio base station judges if there is any variation of the number of radio relay stations when the radio base station carries out transmission through a radio relay station, and the radio base station communicates with the mobile terminal station by switching the multiantenna communication method using the multiantenna depending on the delay time of the feedback signal from the mobile terminal station if there is a variation of the number of radio relay stations.