A control device of a legged mobile robot, wherein a state amount error (for example, an error of a vertical position of a body 3), which is a difference between an actual state amount and a state amount of a desired gait related to a translational motion in a predetermined direction (for example, a translational motion in a vertical direction) of a legged mobile robot 1, is determined, and then a desired motion of the desired gait is determined such that the state amount error approaches zero. The desired motion is determined using a dynamic model by additionally inputting a virtual external force determined on the basis of the state amount error to the dynamic model for generating desired gaits. At the same time, a desired floor reaction force of the robot 1 is corrected on the basis of a state amount error of zero, and compliance control is carried out to make the motion and the floor reaction force of the robot 1 follow the desired motion and the desired floor reaction force of the desired gait.