An allowable ranges of a horizontal component of the translation floor reaction or a floor-surface-parallel component of the translation floor reaction force of a legged mobile robot 1 or a horizontal component of a total center-of-gravity acceleration or a floor-surface-parallel component of a total center-of-gravity acceleration of the robot 1 (hereinafter referred to as a friction force component) is set, and a provisional movement of the robot 1 is determined so as to satisfy a predetermined dynamical equilibrium condition. When the friction force component determined by this provisional movement departs from the allowable range, a rate of change of an angular momentum around the center of gravity of the robot 1 is changed from the provisional movement so as to satisfy the dynamical equilibrium condition while limiting the friction force component within the allowable range to thereby determine a movement of a desired gait. Consequently, not only walking of the robot 1 but also running thereof can be performed properly, and a gait that does not cause slippage is generated.