An electromagnetic actuator for linear driving of movable heads of a magnetic disc unit in an information processing system. A plurality of slits or plates are provided with a magnetic pole inscribed directly on the internal surface of a permanent magnet, and increase magnetic reluctance of the magnetic path and reduce inductance of a moving coil, thus providing shorter positioning time and stable control. In order to obtain the constant strength of magnetic flux and/or torque of a moving coil, said slits or plates have a particular structure.