PURPOSE: To easily set the delay time at every vehicle by automatically obtaining the delay of a right-and-left stereo signal by a mutual correlation corresponding to the change of the shape and dimension of the vehicle, and adjusting the delay time.

CONSTITUTION: A reproduced sound from a sound source 105 is detected by delay detecting microphones 106 and 107 having a directivity for a stereo speaker 103, and provided at a listening position. Then, the mutual function of the detected signal waveform is calculated by a stereo signal mutual correlation calculating part 307, and the delay time between the signal waveforms is searched. Then, the delay time is controlled by variable delay means 205 and 206 provided at each stereo signal forming line system by the output of the calculating part 307, and a sound image at the listening position is corrected. Therefore, the delay of the right-and-left stereo signal is automatically obtained by the mutual correlation corresponding to the change of the shape and dimension of the vehicle, and the delay time is adjusted, so that the delay time of each vehicle can be easily set.