PURPOSE: To permit the miniaturization as well as the speed-up of a disc device by a method wherein side yokes are provided at three sides or at both sides of an upper yoke and a lower yoke as well as the behind side of the same respectively.

CONSTITUTION: A magnetic circuit 21 is constituted of an E-type yoke consisting of an upper yoke 16 and a lower yoke 16', having magnets 11a, 11B, a center pole 22 and a side yoke 19 behind the center pole 22 while a side yoke, not shown in a diagram, is provided at both sides of the E-type yoke. A coil 12, wound around a bobbin 20, is arranged between the magnets 11A, 11B and the center pole 22. The coil 12 is a flat coil and receives a magnetic field B as shown by arrow signs B in the diagram whereby the coil 12 is rotated about a pivot 10. The magnetic circuit of two stages is constituted in such a manner whereby a force, generated by the circuit, becomes more strong than the same, generated by the magnetic circuit of one stage constitution, and the miniaturization as well as the speed-up of the magnetic circuit may be permitted.