Human-robot interaction through music in real environments is essential for humanoids, because such a robot makes people enjoyable. We thus developed a beat-tracking robot which steps, sings, and scats according to musical beats predicted by using a robot-embedded microphone, as a first step to realize a robot which makes a music session with people. This paper first describes the beat-tracking robot, and then evaluated it in detail at the following three points: adaptation to tempo changes, robustness of environmental noises including periodic noises generated by stepping, singing and scatting, and human-robot interaction by using a clapping sound. The results showed that our beat-tracking robot improved noise-robustness and adaptation to tempo changes drastically so that it can make a simple sound session with people.