To provide an acoustic apparatus for a seat audio system allowing a vibration generating means to generate resonance preferred by a user in a seat, irrespective of the type of audio source media.

This acoustic apparatus 1 for the seat audio system has: a vibration generating means 3 provided on the backrest of the seat to generate vibration in response to the signal level of an acoustic signal; an acoustic signal selecting means 11 for selecting an acoustic signal from among a plurality of acoustic signals to be outputted from the different types of audio source media and outputting the selected acoustic signal to the vibration generating means 3; and a control means 14 for controlling a vibration quantity by the vibration generating means 3 in response to the audio source medium of the acoustic signal selected by the acoustic signal selecting means 11.