This letter proposes a tennis instruction support system to provide stroke‐form information obtained through measurement and analysis of ground reaction forces. The originality of the proposed method can be summarized as follows: (i) simultaneous outdoor measurements of ground reaction forces on the front part (toes) and back part (heels) of both feet are conducted for visual recognition of the center of gravity of a tennis player's body during a stroke, and (ii) the comparison between experienced players and beginners is examined so that the system can be used for training beginners. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.