PURPOSE: To improve both efficiency and directivity of a speaker, by setting plural ring-shaped diaphragms on the same axis with those having larger diameters put more backward.

CONSTITUTION: A recess part 11 of a small diameter and a recess part 12 of a large diameter are formed around a center projection part 10 of a bottom plate 9. Cylindrical magnets 15 and 16 are fixed to these parts 11 and 12 respectively, and top plates 17 and 18 are fixed on the magnets 15 and 16 respectively. Then ring-shaped diaphragms 27∼30 containing voice coils 23∼26 formed on polymer films 19∼22 are fixed between the part 10 and the plate 17, the plate 17 and a supporting projected part 13, the part 13 and the plate 18, and the plate 18 and a side wall 14 respectively. The diaphragms 27∼30 are set on the same axis, and those diaphragms having larger diameters are put more backward. Thus it is possible to drive these diaphragms with the same phase.