To automatically attain an optimum sound volume at the time of opening a sunroof or a door window by providing a front seat sound output means and a rear seat sound output means, detecting the open/closed state of an opening/closing part for partitioning an automobile compartment and the outside of it and increasing the sound level of only the front seal output means.

When a passenger opens the sunroof or the door window, it is detected that the sunroof 11 or the door window 12 is open and an H layer is outputted to an OR:13. The OR:13 outputs the H level to a microcomputer 14 at the time of being open. The microcomputer 14 judges that the sunroof or the door window is open and instructs and electronic sound volume 23 to increase the sound volume on a front side for the sound volume set beforehand. As a result, the sound volume of front speakers 251R and 251L is increased and a driver easily enjoy listening with the increase of audio output even when noise is present.