Abstract: A cam plate is pivotably installed to the base plate by means of the pin, the base plate being to be secured to the lateral side of the seat cushion. The base plate has the toothed member pivotable installed thereon, and the toothed member has formed at the free end thereof a cam striker, concavity formed directed from the cam striker toward the base thereof and a projecting release hook contiguous to the end of the concavity. There is also formed on the cam plate a lock cam which supports the cam striker and also slides into the concavity, and a cut is formed in a portion adjoining the toothed member of the lock cam. There is installed to the toothed member a reverse spring which normally forces the lower teeth in such a direction as to engage the upper teeth. When the cam plate is pivoted in one direction, the opposite walls of the cut depresses the release hook. These walls will retain the release hook when the cam plate pivots in the opposite direction.