To provide a device for automatically cutting open side edges of a bound printed product capable of assuring favorable cutting quality in cutting a book or booklet, and applicable even to processing a small number of books or a single product, in which size of the printed products can be very easily changed without changing a press ram or cutting mechanism.

This device is provided with plural cutting stations A, B, and C, and a carrying device 7 to carry the printed product 31 from the first cutting station A to the second cutting station B, and from the second cutting station to the third cutting station C. The open side edges of the printed product 31 are cut by fixed cutters 1, 2, and 3 at the respective cutting stations A, B, and C. The cutting stations are respectively provided with adjustable positioning means 21-24. The printed product is positioned at each station by the positioning means.