Abstract: Provided is an apparatus for modulation in a base station with a smart antenna. The smart antenna system has many advantages that it is possible to deal with the large volume of subscribers; communication quality is increased; etc. However, the smart antenna system has disadvantages that cost is increased due to many antennas; base station transceivers have a complicated structure due to multiple antennas per base station; it is too complicated to manage resource and channel allocation; there is required compatibility with a conventional system; etc. The present invention provides an apparatus for modulation in a base station with a smart antenna, which can solve the foregoing problems by employing a modulator using a time division multiplexing method, a sector beam selector, and a TX beam former, thereby providing good compatibility regardless of a change in the number of base station sectors and the number of antennas.