A prediction model for predicting a mobile robot state is constructed to represent a state change of the mobile robot in a prediction interval of a predetermined duration; time-series data on a control input to ensure stability of the mobile robot is obtained in the prediction interval using a predetermined stability evaluation criterion and a constraint condition based on a mechanical balance; a center-of-gravity trajectory of the mobile robot is obtained based on the time-series data and prediction model; a slack variable for relaxing a constraint is introduced into a constraint condition; a slack variable is introduced into the stability evaluation criterion such that the variable becomes zero when a solution to a stable trajectory is obtained under the constraint condition and a slack variable value is generated when the trajectory diverges under the constraint condition; and positions of contact points are changed so as to cancel the generated value.