The authors performed the experiment by measuring the acceleration of a ship and a human body in the actual ship, and carried out the following statistical analyses on the data: (1) Identification of human responses to the ship's motions. (2) Distribution of forced points acting on the deck through the center of gravity of the human body. Based on the above analyses, results were obtained as follows: (1) A prediction was made of the acceleration response of human body to ship's motion. (2) A 95% probability circle relating to the safety of humans on the ship was obtained.