In this paper, we propose a downlink power control scheme for a wireless system which utilizes a smart antenna technology for space division multiple access(SDMA). In the wireless system which we consider, an access point(AP) forms multiple beams by using multiple antennae and the users of wireless systems get services at the same time by using these beams. By doing so, the spectral efficiency of the wireless system can be increased because multiple data streams can be transmitted at the same time. In this paper, we propose a downlink power control scheme in which the transmission power of each beam is allocated by considering the interference to neighboring APs so that overall system throughput can be improved. Through performance analysis and simulation results, we show that our proposed scheme can increase overall system throughput. We also show that our proposed scheme can improve the throughput even though the information of neighboring APs is inaccurate, which implies that our proposed scheme is robust to errors.