To provide "an audio system", having the spread in sound image having less deterioration of sound field characteristics, even when surround sound reproduction is required.

The audio system has front-mounted speakers 170 arranged on both sides of a front seat; rear-mounted speakers 172, arranged on both sides of a first rear seat more backward than the front seat; rearfill speakers 174, arranged on both sides of a second rear seat farther backward than the first rear seat; a controller 30 which determines whether a voice signal has the number of channels requiring the surround sound reproduction, on the basis of the inputted voice signal IN; and a switch control unit 140 which outputs the voice signal for rear L/R to the rear-mounted speakers 172, when the surround sound reproduction is not required, outputs the voice signal for rear L/R to the rear fill speakers 174, when the surround reproduction is required, and outputs the voice signal for a subwoofer to the rear-mounted speakers 172.