A driving mechanism is provided, including a polygonal base unit, a holder, a first driving assembly, a sensing magnet, and a magnetic field sensor. The polygonal base unit includes a substrate and a circuit board disposed on the substrate. The holder is movably connected to the base unit, wherein the holder is configured to hold an optical element that defines an optical axis. The first driving assembly is configured to drive the holder to move relative to the base unit. The sensing magnet is disposed on the holder. The magnetic field sensor is configured to detect the sensing magnet, wherein the magnetic field sensor is accommodated in a recess of the substrate.