To provide a binding status detecting device for surely detecting a loose bundle in bundles formed by binding the prescribed number of paper sheets.

In a figure 5, (1) shows a case that a normal bundle H1 passes through a binding status detecting device 8A. When the bundle H1 is conveyed, and the top end of the bundle H1 is brought into contact with a rocking safety lug 80, the rocking safety lug 80 is pushed by the bundle H1, and the rocking safety lug 80 is made to rock to a figure E direction. As a result, the bundle H1 passes under the rocking safety lug 80 while its bundle posture does not collapse. In the figure 5, (2) shows a case that a bundle with a loose paper band or a bundle without any paper band passes through the binding status detecting device 8A. In this case, a bundle H2 is not able to shift the rocking safety lug 80, and its own bundle posture collapses, and the length of the conveying direction of the bundle H2 is lengthened. The length of the conveying direction is measured by a transmission sensor 78. As the result of the length measurement, when it is long beyond an allowable value, the bundle H is judged to be abnormal.