PURPOSE: To eliminate labor investigating the thickness of sheet materials by an operator by providing a detection means for detecting the thickness of the sheet materials in a feed route.

CONSTITUTION: A detection means 93 for detecting the thickness of sheet materials 2 is provided in a feed route 9. The sheet materials 2 are perforated by a perforation means 3 and fed to the binding position of a binding member 6 by a feed means 5 and bound by the binding member 6 of a binding means 7. When the sheet materials 2 are set to the feed means at this time, the thickness of the sheet materials 2 is detected by the detection means 93. By this method, with due regard to the capacity of the perforation means 3, the labor investigating the thickness of the sheet materials 2 by an operator can be avoided and the binding work of the sheet materials can be easily performed even by an unskilled operator.