There are provided device for determining a desired trajectory of a translation floor reaction force's vertical component of a legged mobile robot 1, a vertical component of the total center-of-gravity acceleration or a body acceleration vertical component of the robot 1, device for determining a desired vertical position of the total center-of-gravity of the robot 1 or a body 24 thereof so as to satisfy the desired trajectory, and means for determining a desired vertical position of the total center-of-gravity of the robot 1 or the body 24 thereof based on a geometrical condition concerning a joint of a leg 2. Depending on the gait mode, such as walking or running, one of the desired vertical positions is selected, or the desired vertical positions are combined by taking the weighted average thereof or the like, thereby determining a final desired vertical position.