This paper considers an increase in the achievable rate of beamforming systems in two-way communication, resulting from bi-directional use of the spatial resources. The concept of bi-directional use of the spatial resources is first introduced. Then, a condition is derived under which bi-directional beamforming (BB) has larger achievable rate than that of conventional beamforming operating via frequency division duplexing (UB-FDD). In addition, the variation in the achievable rate of bi-directional beamforming is investigated when echo interference is pre-cancelled in the air. Simulation results show that the achievable rate of BB is always larger when the echo is ideally eliminated, and is larger over a certain level of SNR and below a certain level of fading correlation than that of UB-FDD.