Abstract: The present invention relates to a device for retaining knife blades for cutting, perforation or other treatment of a running web, preferably a paper web. The web runs between a rotatable knife-retaining cylinder and a counter pressure cylinder, whereby the knife blade may be wedged up by a wedge device by being brought into the slot by the counter pressure cylinder. In order to permit effective wedging up of knife blades in exact positions in the slot, even when the blades have dimensions which differ from knife blades of the certain defined dimension, the wedge device comprises and/or cooperates with at least one spring disposed beside the wedge device in the slot, upon insertion of a knife blade into the slot for wedging up thereof by the counter pressure cylinder.