Disclosed is a display control device for a touch panel-type setting-operation unit, which is designed to display a plurality of manually operable keys on a display screen and to perform an input processing corresponding to the operation of one or more of the keys. The display control device is operable, based on an evaluation value representing the operational status of each of the keys, which is derived from the relative operation number of each of the keys in a given period of time, to vary the respective display colors of the display areas for the keys in a stepwise manner using a color gradation from a color with high visibility to a color with low visibility in the order of higher score of the evaluation value.