PURPOSE: To surely and effectively report an abnormality message to an operator by temporarily storing the abnormality message from each application function and periodically taking out the stored abnormality message to display it on a CRT.

CONSTITUTION: If an A application function program 11 and a B application function program 12 detect an abnormality, the abnormality message is temporarily stored in an abnormality message storage means 13. A periodical start means 14 periodically takes out abnormality messages stored in the abnormality message storage means 13. Taken-out abnormality messages are successively displayed on a CRT display device by a message display means 15. This abnormality message display means 15 has such function that the abnormality message having the highest priority level is most frequently displayed and abnormality messages having lower priority levels are less frequently displayed. Thus, abnormality messages are surely reported to the operation at the time of the occurrence of abnormality though plural application function programs simultaneously output abnormality messages.