PURPOSE: To restart the display of the display device temporarily stopping the output display for saving energy so as not to generate erroneous inputting.

CONSTITUTION: A photosensor S is provided to detect whether an operator (m) is in front of a display device 4 or not. When there is no detection signal from the sensor S and there is no input operation depending on the operator (m) within installing time, the output display of the display device 4 is temporarily stopped, when the detection signal is outputted from the sensor S, it is judged that the operator (m) takes the input posture, and the temporarily stopped display of the display device 4 is started again. Since the display is not restarted by the key operation of a keyboard 1, no erroneous input is generated.