Humans recognize other persons’ motion and sometimes move our own body including arms, foots and face, imitating the other’s motion. A previous study[1] reported that it was more natural for humans to imitate others’ ipsilateral hand than their contralateral hand. Previous studies reported that the reaction times for identifying objects depend on perceivers’ viewpoint, suggesting that human imitation can also be considered as the process of mental rotation. The purpose of this study is to investigate the spatiotemporal kinetic information in imitated action. We focused on the arm-movement of ‘darts’ action while people were moving their body after learning a specific model’s darts action. All the motion data was obtained by the motion capture system. Right handed participants observed videos of a model and imitated the model with their right hand. Learned videos had following two types. The one was the original video direction, and the other was a horizontally-rotated video of the original clips. The data analysis reported here was focused on the time length of whole/part of each movement. The result suggests that the time of imitated others’ contralateral hand is longer than that of ipsilateral hand, due to the process of mental rotation of their arm direction.