A microphone-unit supporting structure comprises a microphone unit and a holder. The microphone unit includes a substantially-cylindrical microphone element, a printed circuit board fixed to a back of the microphone element, and at least two projections extending radially outward from the printed circuit board and being circumferentially spaced at such an angular interval that when one of the projections is assumed to be on a reference line for line symmetry, the other projection or projections are off the reference line. The holder includes a microphone-unit supporting portion for supporting the microphone unit. The holder has a first groove for receiving first one of the projections, and a second groove for receiving second one of the projections. The first groove is open in a backward direction. The second groove is open in a frontward direction.