PURPOSE: To set and vary parameters through necessary irreducible operation by constituting the parameters in hierarchic structure and providing a means for transition to a parameter except in a higher or lower layer than a displayed parameter.

CONSTITUTION: When a parameter is set, the depression of a menu switch 61 displays a menu screen on a display unit 63, a specific parameter is selected in a displayed parameter group, and a parameter on a low-order side connected to the specific parameter is moved to with an ENTER key 64. Further, the display moves to a parameter group of high order with an EXIT key 65. Further, parameter groups other than the parameter groups of higher or lower order than the displayed parameter group can be moved to by operating JUMP keys 66 and 67. Namely, the display can be moved to relative parameter groups instantaneously irrelevantly to the hierarchic structure of parameters.