PURPOSE: To eliminate the chances of making mis-recognition of effective switches on a panel and to prevent the occurrence of malfunction of a device main body by displaying effective switches among plural switches, which set the operating modes of the device, in accordance with the condition of the device.

CONSTITUTION: An operator panel is provided with a display means 15 which consists of an LD section (a display section) 12, plural switches SW1 to SW5 which set the modes of the device itself and LEDs (light emitting diodes) 13 and 14 and the section 12 displays the state of the device itself, to which the section 12 is mounted, as a message from the panel 11. The switch SW1 is used for function switching and by the operations of the switch SW1 functions F1 to F8 specified by other switches SW2 to Sw5 are switched and this state is recognized by the light of the LEDs 13 and 14 and is displayed on the section 12. Thus, an operator correctly recognizes the effective switches on the operator panel 11 and specifies the objective functions without errors.