a display device has a display panel in which patterns are impressed in conformity to the layout of a master instrument . with this display device , a pattern indicating a prescribed condition of the master instrument which is to be detected and a pattern representing a countermeasure for the prescribed condition are impressed on the display panel . patterns related to the conditions of the master instrument which can be coped with without cutting off a power switch are displayed in a first color and patterns related to the conditions of the instrument which cannot be coped with unless the power switch is cut off are displayed in a second color . when particular conditions of the master instrument are detected , then patterns denoting the detected conditions and patterns representing countermeasures for the detected conditions are visually indicated to teach the operator to take a proper action .