PROBLEM TO BE SOLVED: To provide a communication system and a base station, capable of achieving base station transmission beam forming using an array antenna without providing an estimation device in a radio wave arrival direction and a transmission-system calibration device in the base station.SOLUTION: A first base station 21 receives communication quality information from a first mobile station 31, estimates a precoding candidate for a second mobile station 32 which can reduce interference from a second base station 22 in the mobile station 31 on the basis of the communication quality information, and transmits the precoding candidate to the base station 22. The base station 22 receives a precoding candidate for the mobile station 31 from the base station 21 and estimates communication quality when the precoding candidate is set. When the estimated communication quality exceeds a preset predetermined communication quality, the base station 22 changes the precoding set in the mobile station 32 to the precoding candidate received from the base station 21.