A base station 20 monitors change of a parameter for an adaptive array antenna, the parameter being used to control a directivity of a beam to be transmitted to a mobile terminal device 30. As a result, when detecting that a value indicating the change has fallen below a predetermined value, the base station 20 suppresses control of the directivity of a transmission signal. Moreover, the base station 20 transmits decrease information to the mobile terminal device 30, the decrease information indicating that the value indicating the change has fallen below the predetermined value. Upon receipt of the decrease information transmitted from the base station 20, the mobile terminal device 30 equalizes a signal to be transmitted to the base station 20 on the basis of a delay status of a reception signal received from the base station 20, and then transmits the equalized signal to the base station 20.