PURPOSE: To obtain an eccentric motor excellent in efficiency and controllability generating high torque, by filling up a magnetic space between a stator and a rotor, with magnetic fluid.

CONSTITUTION: A magnetic space 9 between a stator 1 and a rotor 2 is filled up with magnetic fluid 6. The whole area of the space 9 may be not always filled up with the magnetic fluid 6. A permanent magnet 7 existing in the rotor 2 is mainly for retaining the magnetic fluid at the time of non-excitation, but a magnetic force due to magnetic flux generated from the permanent magnet 7 and magnetic flux generated from the stator 1 may be used. The permanent magnet 7 is not always necessary if the other means of sealing or the like is used as the retaining means of the magnetic fluid 6.