The designation of a localization position is received in accordance with an input position on a dashboard image in a localization-position reception window, and delay times for audio signals supplied to respective speakers are set so that the sound image is localized at the received localization position. The position where a sound image aurally perceived is localized is received, on the dashboard image in a localization-position confirmation window, from the user, until the user indicates that the position where the sound image aurally perceived is localized matches the localization position designated in the localization-position reception window. The relationship between the delay times and the localization position is re-estimated so as to correspond to the received localization position and the set delay times. In accordance with the estimated relationship, processing for re-setting the delay times is repeated.