A speaker unit mounting structure includes a provisionally fastening mechanism for fastening a speaker unit to a ceiling with a cabinet section of the speaker unit inserted in a mounting hole of the ceiling. The provisionally fastening mechanism includes a provisionally fastening tab formed of resilient metal, fixed to the outer peripheral side surface of the cabinet section and having a stepped engaging section engageable with the inner peripheral edge portion of the mounting hole. Engagement of the engaging section with the inner peripheral edge portion of the mounting hole can be canceled by a human operator pressing, from the face side of the ceiling, an operating section of the tab, exposed to a gap between the front side and a flange portion of the speaker unit, to thereby resiliently deform the operating section.