A control device for a walking assist device is provided. The control device has a means that decides whether the total sum of measured values of treading forces of the legs of a user is greater than a predetermined value and a means which determines a predetermined ratio according to observed values or desired values of reference parameters obtained immediately before a negative determination result by using supporting forces acting on the leg links from the floor side as the reference parameters. This is in the case where the determination result of the decision means is negative and is a process undertaken instead of determining the predetermined ratio between the supporting forces acting on the leg links according to the measured values of the treading forces of the legs of the user.