In an apparatus for generating clamping force in injection molding machines having stationary and moving platens, between which an injection molding die is mounted, and a traversing mechanism associated with the moving platen for opening and closing of the injection molding die, the present invention provides means for locking the traversing mechanism after the molding die has been closed. The clamping force required during injection is generated by at least one element made of a magnetostrictive material that is mounted between the traversing mechanism and the moving platen. Each magnetostrictive element is surrounded by a magnetic coil that is controllably energized to produce an alternating magnetic field which causes elongation of the associated element, generating the clamping force.