In ballroom dance leader (male) dances with partner (female). The skills for pair dancing has not been investigated. The purpose of this study is to investigate movement interaction between the leader and the partner during ballroom dancing. The world competitive ballroom dance champion couple participated in the study. The Xsens system consisting of inertial measurement units was used to measure body positions at 240 Hz. The participants danced waltz under three conditions. The leader danced by himself. The partner danced by herself. The leader and the partner danced together. In particular, the movement interaction was found in kinetic energy.