A driving device including a magnetized driving rotor mounted for rotation within a magnetic field produced in a coreless coil, and, in order to make the magnetic pole of said driving rotor deviate by a definite angle relative to the magnet field direction of said coil, a supplementary magnetized rotor mounted for rotation outside of the coil and magnetically coupled with the driving rotor. And the supplementary rotor is provided with magnetic poles, the number thereof being greater than the number of poles of said driving rotor. The driving rotor has an odd number of pole pairs.