PURPOSE: To simplify the structure of the subject device and contrive the improvement of reliability by counting the number of the pulse of the pulse signals generated at the intervals of the two successive signals for detecting the passage of folded papers to compare it with a preset value.

CONSTITUTION: Printed web paper W is fed between a cutting cylinder CC and a folding cylinder FC rotating in opposing relation to be cut and folded into a predetermined length and thus cut pieces are successively run off from the cylinders as folded paper S. When the folded papers S are passing between a light projector 21 and a light receiver 22, the light is intercepted but reaches the light receiver 22 through gaps between a successive series of the folded papers S to produce voltages. The changes in voltage thus taking place are sent to a comparative judging part 31 as folded paper passing signal. On the other hand, a pulse signal is generated by a pulse signal detecting means 1 according to the rotation of the main shaft of a motor and sent to the comparative judging part 31. The number of the pulses is counted for the periodic passage and let-off of the fold papers S to be compared with the values preset by a preset input part 32. If the number of the pulses reaches at least the preset value, an abnormality signal is generated by an abnormal signal generating means 3.