An acoustic device that provides a stereophonic effect to a driver of a mobile object includes: a plurality of speakers (an L channel speaker and an R channel speaker) mounted on a steering wheel that controls a traveling direction of the mobile object; a steering angle detection unit configured to detect a steering angle of the steering wheel; and a signal output unit configured to output a plurality of output signals obtained by performing, on a sound signal, a process relating to the stereophonic effect and depending on the steering angle, respectively to the plurality of speakers.