Disclosed is an apparatus for forming a downlink traffic beam in a base station that separately forms a traffic beam for each user using multiple antennas. In the apparatus, an instantaneous direction estimator detects a signal having maximum energy and an energy value from a received uplink signal. A downlink spatial correlation matrix update unit calculates a downlink spatial correlation matrix using an output value of the instantaneous direction estimator and a downlink antenna direction response characteristic. A beam vector adaptation unit outputs a downlink bean-forming vector by reflecting a phase difference between a common beam and a traffic beam from an output of the downlink spatial correlation matrix update unit.