PURPOSE: To prevent the run-out of a paper from occurring, by providing a means for detecting printed lines on the basis of the input of a predetermined signal and a means for detecting residual lines on a printing paper, and operating an alarm device and a display device based on an output signal from the latter detecting means.

CONSTITUTION: A printed lie detecting means for detecting the lines printed by a printer 5 on the basis of the input of a predetermined signal and a residual line detecting means for detecting the condition where the number of residual lines on a printing paper is reduced to or below a predetermined value are provided, and alarm devices 1a, 1b and a display device 7 are operated based on the output signal from the residual line detecting means. Alternatively, when the paper is fed, the duration of feeding is measured, the measured value is converted into a number of printing lines, the number is added to the value in a counter, the period of time for which a printing signal is outputted is measured and the number of printed lines is analogized, whereby the amount used may be displayed on the display device in place of the residual amount. Accordingly, the run-out of the printing paper can be prevented through the alarm device or the display device.