To provide a horn speaker having a flat reproduction frequency characteristic with a diaphragm curved in a concave shape in a sound emitting direction.

In a horn speaker, a diaphragm 17 is supported behind a phase plug 16. When the diaphragm 17 oscillates, air in a sound generation space OS between the diaphragm 17 and the phase plug 16 is pushed out to slits 21 and 22 in the phase plug 16, and sound wave is emitted from a horn 14. Separation plates 50 are provided on an outer peripheral surface 42 of the phase plug 16. The separation plates 50 insulates the sound generation space OS from a space AS surrounded by the phase plug 16, a pole piece 10, a back plate 31, an annular magnet 32, a top plate 33, a spacer ring 34, and an edge 40.