An allowable range of a frictional force component, such as a horizontal component of a translation floor reaction force, applied to a legged mobile robot 1 is set, and a provisional movement with a current time gait of the robot 1 is determined so as to satisfy a condition concerning the allowable range and a dynamical equilibrium condition that a moment produced about a point of application of a provisional desired floor reaction force substantially agrees with a provisional desired floor reaction force moment. The provisional movement is determined by adjusting movements in two movement modes which are different in ratio between the translation floor reaction force and the floor reaction force moment. Based on the final state of the provisional movement, the current time gait is determined by correcting the provisional movement and at least one of the point of application of the provisional desired floor reaction force and the provisional desired floor reaction force moment in such a manner that the current time gait is connected to or brought close to a normal gait. The correction is performed when the frictional force component is unlikely to exceed the allowable range.