PURPOSE: To improve the detection accuracy by logically calculating the outputs of sensors detecting the rotation angle of the drive shaft of a kicker pushing the lowermost layer of many stacked corrugated board sheets and the transit and inclination of the sheet directly after feed rolls.

CONSTITUTION: Many sheets 11 are mounted on a receiving plate 12 and are positioned by a front gate 13 and a back stop 14. A mobile body 17 on a base 15 is moved back and forth by a lever 21 fitted to the crank plate 20 of a drive shaft 19, and the lowermost layer sheet 11 is pushed between feed rolls 16 by a kicker 18. The rotation angle of the drive shaft 19 when the kicker 18 is operated is determined by a piece 23 fitted to the drive shaft 19 and a sensor 24. The transit of the sheet 11 is detected by a sensor directly after feed rolls 16. The sheet 11 is transferred 26, 27, and the parallel displacement, right inclination, left inclination of the sheet are detected by sensors 29, 30, 31 at the entrance of a printing unit 28. The outputs of the sensors 24, 25, 29W31 are logically calculated, and an alarm is generated in case of abnormality. Accordingly, the abnormality detection is automated and its accuracy is improved.