An articulated motion estimating unit stores in advance angle information, angular velocity information, and torque information for each joint of an articulated object. Assuming that torque changes are constant, the articulated motion estimating unit predicts motion by repetition of an updating process and a prediction process. In the prediction process, the present cycle angular acceleration is computed based on stored information using a dynamics equation. Then, the next cycle angle and angular acceleration are computed based on an ordinary differential equation. Finally, the next cycle estimated error covariance is computed, and the next cycle motion is thereby predicted.