A paper conveying device of the present invention includes a roller to convey paper, a first and a second sensors to detect the paper conveyed through the roller and a timer to measure a time required from the time when the first sensor detects the paper until the second sensor detects the paper. It is judged whether the time measured by the timer is exceeding a prescribed set value and based on this judging result, the number of times exceeding the prescribed set value is counted by a counter and the life of the roller is judged based on the counted number of times exceeding the prescribed set value.