An earphone 1, which adopts the drum air power system the invention, includes at least a drum 5 composed of a drum-shaped casing 2, a front head 3 located on the front part of the casing 2, a rear head 4 located on the rear part of the casing 2, an inner-drum space 5a defined by the casing 2, the front head 3, and the rear head 4. Earphone 1 also comprises a driver unit 6 installed inside the drum 5 and equipped with an external sound conducting part 6a and an internal sound conducting hole 6b. The front head 3 and the rear head 4 resonate in response to driving by the driver unit 6 so that the low pitch sounds B and C are output in addition to the full range sound formed from the external sound conducting part 6a. This structure lowers the minimum resonance frequency and increases the sound pressure.