In an in-vehicle mount type AV system for implementing proper acoustic effect control, a swing angle of a rear monitor is detected by a right and left angle sensor, and respective acoustic effects of four speakers (for example, the volume levels of reproduced sounds) are adjusted. The angle detected by the right and left angle sensor corresponds to the angle of the display face of the rear monitor, and the correlation between the display face and the head position of an occupant (automobile passenger) can be estimated. That is, the probability that the head portion of the occupant exists in a direction to which the display face of the rear monitor is oriented is high, and thus the acoustic effect is controlled so that proper volume balance is established at the occupant position thus estimated.