The present invention provides a speaker mounting structure that takes up less space and affords easier mounting. A mounting component 6 of a speaker 2 is provided to the rear pillar 3 of an automobile 1. A quarter inner panel 7 is provided on the interior IN side of this speaker mounting component 6, and a side body outer panel 8 is provided on the exterior OUT side, leaving a specific gap 9 in between. An extension panel 10 is attached on the exterior side OUT of the quarter inner panel 7. A through-hole 14 is formed in the quarter inner panel 7 and the extension panel 10, and the rear end 12 of the speaker 2 is inserted into the through-hole 14. As a result, the speaker 2 is moved further to the exterior OUT of the cabin, so the trim piece 16 does not protrude as far into the interior IN and rearward visibility is improved.