To reduce erroneous detection of a jam, since there is risk of damaging an actuator in work by inferiority in workability due to a hindrance by the actuator, when performing continuous paper removing and refolding work, when the jam is caused.

This image forming device has a jam discriminating means discriminating folding failure of continuous paper P on the basis of light receiving time when a light receiving part 6 receives the inspection light 3 and light shielding time when the inspection light 3 is shielded by the continuous paper, that is, the jam discriminating means discriminating the folding failure of the continuous paper P on the basis of a detected result by a paper sensor SN of a short continuous paper detecting position when using short continuous paper of the short paper length, and discriminating the folding failure of the continuous paper P on the basis of the detected result by the paper sensor SN of a long continuous paper detecting position arranged above an arranging position of a light emitting part 4 and a light receiving part 6 of the short continuous paper detecting position in at least one of the light emitting part 4 and the light receiving part 6 when using long continuous paper of the long paper length.