PURPOSE: To attain easily the display of a key corresponding to the contents of function set by the user, by providing a display section representing the contents of function and making easily the display contents exchangeable.

CONSTITUTION: In the figure, 1 is a function selecting key and a prescribed function is called by transmitting a signal with depression. The function selecting key 1 on an operating panel A is provided with a recess 1a on its upper surface. Display plate 21 or 22 displaying the function is inserted to the recess 1a. The plates 21, 22 are exchangeable with each other, and when they are made of a transparent member, they can be placed on the recess 1a by overlapping them. Further, on the key 1 with the plate 21 an inserted box shaped transparent cap 3 is fitted detachably and attachably. Thus, the dirt and the missing of the display plates are prevented.