Abstract: An apparatus for retaining a boot on a ski including a mobile lock adapted to be displaced between a retention position and an open position. In the retention position the the lock retains the boot on the ski. In the open position the lock permits the boot to be disengaged from the ski. Also provided is a generally upside down U-shaped spring in the form of a stirrup having a two ends which are pivotally attached to the ski and a median portion including a projection which extends toward these ends and which is adapted to be displaced on the surface of the lock. Both the lock and the spring are pivotally attached to the ski around different transverse axes so that the lock and the spring form a toggle mechanism. As a result, when the projection is displaced on the surface of the lock to one side of a plane passing through the two transverse axes, the lock is biased and displaced into one of its two positions.