A filter coefficient of a graphic equalizer GEQ is corrected based on detection results of reproduced sounds generated by supplying a noise to all frequency band loudspeakers 6 FL to 6 RR and a low frequency band exclusively reproducing loudspeaker 6 WF via the graphic equalizer GEQ. Then, attenuation factors of channel-to-channel attenuators ATG 1 to ATG 5 are corrected based on the detection results of the reproduced sounds generated by supplying the noise to the loudspeakers 6 FL to 6 RR via the graphic equalizer. Then, delay times of delay circuits DLY 1 to DLY k are corrected based on the detection results of the reproduced sounds generated by supplying the noise to the loudspeakers 6 FL to 6 WF via the graphic equalizer. Then, an attenuation factor of a channel-to-channel attenuator ATG k is corrected based on the detection results of the reproduced sounds generated by supplying the noise to the loudspeakers 6 FL to 6 RR via the graphic equalizer and the detection result of the reproduced sound generated by supplying the noise to the loudspeaker 6 WF via the graphic equalizer, whereby levels of the reproduced sounds reproduced by the loudspeakers 6 FL to 6 WF are adjusted to be made flat over the audio frequency band.