A microphone unit comprises a vibratory diaphragm for detecting sound input through its first and second openings. The sound input through the first opening is guided to a front surface of the vibratory diaphragm while the sound input through the second opening is guided to a rear surface of the vibratory diaphragm so as to detect the sound by the vibration of the vibratory diaphragm. The microphone unit satisfies relation 0.76≦D/Δr≦2.0 where D is difference in time between the sound propagation time from the first opening to the front surface of the vibratory diaphragm and that from the second opening to the rear surface of the vibratory diaphragm, while Δr is distance between the first and second openings. The relation D/Δr≦2.0 can reduce far-field noise, while the relation 0.76≦D/Δr can increase the detection sensitivity to sound emitted from a null point.