A tone generating apparatus has an internal storage in which defining information (taking the form of table information, for instance) on relationship between operation conditions of the apparatus and applications of operation members, such as slider, switch and encoder, is stored in advance. CPU of the apparatus controls the apparatus in such a manner that applications of operation members in a current operation condition of the apparatus are effected according to the defining information. With this arrangement, the work for changing specifications of the apparatus is simplified since it is done primarily by changing contents of the defining information.