To provide a motional feedback (MFB) acoustic device capable of obtaining excellent sound quality by a simple configuration.

An audio signal is inputted to a positive side input terminal of a differential amplifier 1, a vibration speed detecting signal from a vibration speed detection coil 5 for detecting the vibration speed of a voice coil 4 in a speaker 3 is inputted to a negative side input terminal, and the differential amplifier 1 outputs a differential signal in accordance with a potential difference between the input audio signal and the vibration speed detecting signal. An MFB level adjustment section 6 changes the level of the differential signal from the differential amplifier 1 in accordance with a resistance value set according to user operation, and a power amplifier 2 amplifies the differential signal changed by the MFB level adjustment section 6 and vibrates the voice coil 4 of the speaker 3.