This paper proposes a combined scheme in which adaptive beamforming and acoustic echo canceller are integrated in order to achieve a robust full-duplex speech interface between user and mobile robot. In particular, this paper addresses the situation in which an echo signal and the user's voice are propagated from the same direction toward a linear array of microphones. We propose a cascading scheme that uses an acoustic echo canceller followed by an adaptive beamformer. By using the system output to adapt echo canceller, and by controlling the adaptive mode of each adaptive filter in the beamformer and in the echo canceller, we can recover the original speech, which would otherwise have remained contaminated by both noise and echoes. In addition, a double-talk detector is proposed so that effective acoustic echo cancellation may be attained without generating error divergence when the user's voice and the echo are present simultaneously. Representative experimental results with real data demonstrate the validity of the proposed scheme.