The binder mechanism for loose-leaf binders or file folders comprises a flat, oblong support plate on which are disposed at a standardized mutual distance at least two binder yokes, each consisting of a fixed yoke rod and pivotable yoke part, which is provided with a crank arm. The pivotable yoke parts are operable jointly because they are interconnected by a coupling rod disposed in the support plate. The support plate is made of plastic and has a cavity which is open at its underside and in which the crank arms and the coupling rod are accommodated. The privotable yoke parts are mounted in mounting bushings integrally molded to the likewise plastic crank arms mounted in hollow cylindrical bearing lugs or bearing holes of the support plate. The coupling rod and/or at least one of the crank arms are associated with a releasable detent or locking device which arrests the movable yoke parts jointly in their pivoted position forming the yoke shape. Advantages include: simple and low-cost production, easy handling, great functional reliability.