Abstract: It is an object of the present invention to provide an irregular feeding detection device and a detection method of irregular feeding having high detection precision.The irregular feeding detection device is a device to detect irregular feeding of printing paper 10 (the printing papers overlapped partially or overlapped completely) fed to a direction shown as arrow 90 in a printing machine. An transparent light amount detector 2b carries out a plurality of detection with predetermined interval when the printing paper 10 reaches to the predetermined starting position (FIG. 5A). Thus, the amount (value) of detecting light at a plurality of the detecting places (P1, P2 and P3) can be detected. For instance, when at least two pieces of printing papers are fed into the device, irregular feeding signal are outputted since the irregularity of feeding is detected at least two detecting places.