An in-car audio system includes a speaker unit. A frame of the speaker unit is fixed to a support plate serving as part of the structural member of a vehicle via a partition wall member. The support plate has an opening formed therein. A duct is connected to the opening, and the opening communicates with the outside of the vehicle. A space surrounded by the speaker unit, the support plate, and a partition wall member serves as a first acoustic resonance space, and a communication channel located inside the duct serves as a second acoustic resonance space.