A control system for a walking assist device includes a ground detecting means having a plurality of force sensors equipped to each foot attachment portion. Each ground sensor selectively outputs a ground state output and non-ground state output in accordance with whether the foot attachment portion is grounded at a position immediately below the ground sensor. The control system is equipped with a means that continuously generate preference data for each of the ground detecting means, where the reference data increases and decreases in value in accordance with the change of a total number of the ground sensors generating ground state output in the ground detecting means. Also, a means that determines a mutual desired proportion of the supporting force to be applied to the both leg links from the floor side is provided.