A noise-reducing headphone includes a headphone housing, a speaker unit, and a microphone. The headphone housing includes an accommodating space and a sound output hole. The accommodating space is communicated with the sound output hole. The speaker unit is positioned in the accommodating space. The speaker unit includes a speaker unit housing and a diaphragm disposed on the speaker unit housing. The diaphragm faces toward the sound output hole and includes a central through hole and an annular vibrating portion around the central through hole. The diaphragm produces sound waves toward the sound output hole by vibrations of the annular vibrating portion. The microphone is disposed on the speaker unit housing and is positioned in the central through hole. The microphone is coaxial to the central through hole. One face of the microphone faces toward the sound output hole and the other faces toward the inner of the headphone housing.