A mobile communication base station determines the oncoming direction of a radio wave with a simple arrangement and transmits a narrow angle beam in this direction. Received signals from a pair of wide angle beam antennae 21-1 and 21-2 having an equal configuration and a common orientation and which are located close to each other are fed to a direction finder receiver 22 and a communication receiver 15. By utilizing the fact that the both received signals have a coincident amplitude, a phase difference between the received signals is detected. The oncoming direction of the received radio wave (or the direction of a mobile station) is determined on the basis of the phase difference. A beam switcher 12 is controlled so as to connect a transmitter 13 to a narrow angle beam antenna (one of 11-1 to 11-4) which is directed in the oncoming direction thus determined.