To intuitively grasp the picture corresponding to a processing where a fault has occurred by displaying the picture corresponding to the processing where the fault has occurred among pictures in the foreground and displaying a fault occurrence notification picture as a different picture over the picture.

If a fault occurs in processing execution, a fault detecting means detects the fault and passes information specifying the contents (i.e., error or alarm) of the fault and information specifying the picture corresponding to the processing where the fault has occurred to a picture control means, which displays the picture 12 corresponding to the processing where the fault has occurred in the foreground of the display device (a). Then the fault notification picture 14, i.e., an error or alarm notification picture is displayed over the picture 12 displayed in the foreground. Consequently, it can intuitively be grasped which picture the processing where the fault has occurred corresponds to.