To provide a medium bundling device for detecting defective bundled state of a bundle after bundle processing is completed in the device for bundling processing with a paper band.

The device is provided with: a bundling means for performing bundling with a paper band provided with prescribed patterns; a paper band feeding means for supplying the bundling means with paper bands; a printing means for printing the specified patterns onto the paper bands for bundling; an image reader for reading an image on the surface of the paper bands; and a determination means for analyzing the image on the surface of the paper bands read by the image reader to determine the quality on the basis of position relations of the patterns.