A device for processing a printing substrate (22), having at least one processing tool (10), in particular a die plate or a perforating knife, which is accommodated on a rotatable carrier body (14); the carrier body (14) being at least partially provided with a magnetizable coating (16) which, when magnetized, holds the processing tool (10) on the carrier body (14) by the action of magnetic force. The device can be used to advantage in a print finishing machine, a printing press, or in a folding apparatus of a web-fed printing press.