To predict the behavior of a predicted object with high precision.

Behavior history information on the predicted object is obtained and on the basis of the obtained behavior history information, unit behavior history information on the predicted object is extracted to generate unit behavior history information of a group of predicted objects and on the basis of the unit behavior history information on the predicted object and the unit behavior history information on the group that a predicted object joins in, the behavior of the predicted object is predicted. Consequently, the unit behavior history information used to predict the behavior of the predicted object can be increased as compared with a case wherein the behavior of the predicted object is predicted by using only the unit behavior history information on the predicted object, thus actualizing the behavior predicting method and its device which can predict the behavior of the predicted object with high precision.