PURPOSE: To automatically set and change an equalizing characteristic corresponding to the change of an acoustic characteristic in a room while listening to music, and travelling.

CONSTITUTION: A music signal S(t) from an audio source 11 is outputted from a speaker 14 to a sound field, a sound in the sound field is detected by a microphone 15, and signal components Xi(t) and Si(t) in each band of a microphone detection signal X(t) and the music signal S(t) are extracted by each band pass filter 16 and 17. Then, respective band pass filter outputs Xi(t) and Si(t) in a prescribed band are inputted to music signal magnification measuring parts 180-18n, the music signal components multiplied by a coefficient βi, and the microphone detection signal components multiplied by the coefficient βi are respectively differentiated, and the coefficient βi is decided so that a difference between both the differentiation signals can be reduced and the coefficient βi is outputted as a magnification. A controller 19 finds an integrated frequency characteristic by using the magnification βi in each band, and changes the characteristic of an equalizer 12 so that the integrated frequency characteristic can be the desired frequency characteristic.