PURPOSE: To eliminate the occurrence of reverberatory sounds peculiar to car rooms and, at the same time, to form an extensive sound field by providing a means which passes frequency signals below a fixed frequency of the added signals of left and right output signals or either the left or right signals and supplies the frequency signals to a left or right side loudspeaker.

CONSTITUTION: Reverberatory sounds peculiar to a car room are produced by standing waves of a frequency decided by the internal dimensions of the car room. Especially, standing waves of about 200 Hz in frequency produced by the transversal dimension of the car room more affects the occurrence of the reverberatory sounds. Therefore, in order to reduce the influence of the transversal dimension, signals of one channel of a pair of door loudspeakers 11R and 11L are reproduced through a phase shifter 30. Therefore, signals of a fixed low frequency are separated from those of a frequency related to the localization of a sound image and the sound image does not become unclear, because the signals of the fixed low frequency enter the left and right ears of a listener in reverse phases. Therefore, the reverberatory sounds peculiar to car rooms can be eliminated and a sound field which gives a clear feeling of low-pitched sounds and has a natural extent can be formed.