A motion estimation system 80 includes a pose acquisition unit 81 and an action estimation unit 82. The pose acquisition unit 81 acquires, in time series, pose information representing a posture of one person and a posture of another person identified simultaneously in a situation in which a motion of the one person affects a motion of the other person. The action estimation unit 82 divides the acquired time series pose information on each person by unsupervised learning to estimate an action series that is a series of motions including two or more pieces of pose information.