A lens driving module is configured to provide an imaging lens system with auto-focus functionality. The imaging lens system is disposed between a preloading element and a driving base of the lens driving module. The preloading element includes an injection molded part and a ferromagnetic part partially embedded in the injection molded part. A rollable element is disposed in each of mounting structures of the injection molded part and in contact with a displaceable lens carrier of the imaging lens system. The ferromagnetic part and a magnet disposed on the displaceable lens carrier together generate a magnetic attraction force, such that the displaceable lens carrier exerts a preloading force on the rollable element. The driving base includes a driving coil and an electrical wiring pattern. The driving coil corresponds to the magnet for generating a driving force to drive the displaceable lens carrier to move along the optical axis.