PURPOSE: To provide a method and device for detecting paper roll residual amount capable of managing at all times the residual amount of paper roll under usage by detecting the initial residual amount of paper roll to be used upon setting of paper roll.

CONSTITUTION: A lever 2 arranged at a residual amount detection mechanism 1 is fixed to a shaft 4 and the shaft is adapted to turn freely. The lever 2 is energized in the arrow A direction by a spring 3, and thus it abuts against the outer dia. of a paper roll 7. A position detector 6 is arranged on the side of a plate 2a of the lever 2, and thereby the specified position of the lever 2 is detected. At the shaft 4 a displacement detector 5 for detecting the rotation displacement of the shaft 4 in the arrow F direction is set.