A function setting method for an audio system which is capable of changing a function of the audio system without alternation of hardware of a system controller at all and is superior in general use. The method comprises the steps of preparing, as the system controller for controlling functions incorporated in the audio system in a concentrated manner, a microcomputer which has an analog/digital conversion input port and has built therein control programs for all of a plurality of functions which can be incorporated in the audio system, and applying a selected one of a plurality of analog voltages which individually represent possible combinations of the functions including the individual functions to the analog/digital conversion input port of the microcomputer to cause the microcomputer to be prepared for one or ones of the functions represented by the analog voltage.