An acoustic system comprises an operation condition determination part for determining an operation condition of an operating element for controlling sound volume of a sound reproduction device which reproduces sounds from a plurality of sound sources, and a control part for changing a control object of the sound volume by the operating element in accordance with the sound source which is reproduced by the sound reproduction device, based on the operation condition determined by the operation condition determination part. The control part prohibits switching of the control object of the sound volume by operation of the operating element even when the sound source to be reproduced has been changed while it is determined by the operation condition determination part that the operation of the operating element is continuously performed.