In this paper, we propose a system which plays an appropriate beat music to dance, which is one of emotional self-expressions using human motions. Dancers presently have a limitation on their expressions because they have to determine their rhythm considering given music; we believe that dancers can express their own emotions more freely without the consideration. The proposed system focuses and obtains “the human motion rhythm,” and automatically plays a beat music based on the rhythm. In this paper, we conducted comparative experiments for extracting rhythm method: the method focusing on “periodicity of human motions” and “key poses: the stop motions.” Performance evaluation results showed that the beat music played by the proposed system focusing on periodicity of human motions was well harmonized with the human rhythmic motion for a beat per minute, and it worked well for different human motions. Results of subjective evaluation suggested that the proposed system played the beat music which rhythm was appropriate to the dance.