It is an object of the present invention is to smoothen air flow at the time of vibrations of the diaphragm, and to suppress variations in acoustic characteristics. Since the inclined surface 37c of the washer 37, which forms the air flow channel 50, is an inclined surface having a diameter gradually reduced with distance from the diaphragm 35 in the axial direction of the movable iron core 36, compared with the conventional step-shaped air flow channel having vertical surfaces, air flow in the air flow channel 50 can be smoothened. Therefore, disturbance in air flow is not easily generated in the air flow channel 50, and variations in acoustic characteristics of the horn apparatus 10 can be suppressed.