PURPOSE: To obtain an accurate linear part, by constituting a driving unit suitable for the large-diameter plane diaphragm and by storing the voice coil in the magnetic gap fully with accurate dimensions, in respect to the voice coil used for the angular plane diaphragm speaker unit.

CONSTITUTION: For voice coil 20, long ribbon-shaped foils 21a, 21b, 21c and 21d obtained from the conductive material slightly narrower than the width dimension of magnetic gap 15 are used correspondingly to the width dimension of magnetic gap 15. These foils 21a and so on are formed into a lamination state, and linear parts 22 and corner parts 23 where linear parts 22 intersect orthogonally are provided. In respect to these foils 21a and so on, slits 21b where one end parts are not opened alternately at a fixed interval from both width directions are provided in foil material 21a of the width dimension corresponding to linear part 22, and these slits are extended, and they have the surface and the reverse face inverted and are folded orthogonally in continuous part 21c, and this inversion and folding is repeated up to a prescribed number of turns, and further, protrusion part 21d protruded to corner part 23 is removed by cutting, thus obtaining coil 20. As a result, coil 20 can be stored in the magnetic gap fully with accurate dimensions to provide the linear part accurately.