Abstract: A magnetic rotor (3) of suitable configuration is supported so that it is free to rotate in a vessel or tube, whereby the rotor is in direct contact with the stirred or pumped medium and is rotated by the rotary magnetic field of an electromagnetic drive system (2). The rotary magnetic field is generated by a number of coil segments (6,6',6",6"') controlled by phase-shifted alternating currents (8,8'), whereby the coil segments are arranged on an annular core (4) of ferromagnetic material. With the appropriate arrangement and control of the coil segments, the rotor located near the ring axis turns very smoothly, since the presence of individual magnetic poles can be dispensed with. The annular design of the core also allows stirring to be performed in a vessel with a central outlet at the bottom. The electromagnetic drive device (1) together with its core and winding, which require only one cable lead connection to the power source arrangement (1), can be of compact, leakproof and chemically resistant design.