A driving device for driving two door panels to synchronously move has a rail rod, an endless cord and multiple clamping assemblies. The endless cord is parallel to the rail rod and is mounted at a position at inner sides of the door panels. The clamping assemblies are securely connected to the cord, are moveable relative to the rail rod and clamp the door panels. Each clamping assembly has a front clamping panel and a rear clamping panel. The front clamping panel is mounted on an outer side of a corresponding one of the door panels. The rear clamping panel is mounted on the inner side of the corresponding door panel and is connected securely to the front clamping panel and the cord. Accordingly, the conjunction positions between clamping assemblies and a cord are hidden by the inner sides of the door panels.