PURPOSE: To give a warning in a manner easily calling their attention at the time of necessitating the intervention of operators in a printing apparatus.

CONSTITUTION: When the main controller 2 detects any hindrance, it outputs signals to make lights glimmer relative to the rear illumination part 7 of a display 6. Simultaneously, it outputs signals even to a frequency switching part 9 to give a warning from a sounding part, 10 at higher frequency than ordinary sound. Besides, it is acceptable to provide a light source with different colors on the rear illumination part 7 and change it over, and also acceptable to increase sound volume instead of frequency in the sound emitted by the sounding part 10.