A fader device used for an audio mixer etc. includes fader operators, a signal processing circuit for processing signals in accordance with operation position of the fader operators, switches for switching an operation mode of fader operators between an absolute mode in which amounts of displacement of the fader operators represent absolute change value and a relative mode in which amounts of displacement of the fader operators are caused to represent relative change values by setting a predetermined displacement range of a control parameter. When the operation mode has been switched from the absolute mode to the relative mode, a control circuit peforms control in such a manner that the amounts of displacement of the fader operators in the absolute mode have been stored and the fader operators are forced to be set in central positions of the strokes of the fader operators. Total amount of operation is recognized by calculating the stored value corresponding to the central position and displacement value from the central position. The amounts of displacement of the fader operators in the relative mode can be controlled at a smaller ratio than in the absolute mode and a fine adjustment of a signal level thereby can be achieved.