An apparatus for detection of the accuracy of format of a web of corrugated cardboard moved in a conveying direction comprises a light source which emits a light band to the surface of the web of corrugated cardboard in a direction crosswise of the conveying direction and at an angle to the web of corrugated cardboard. A measuring camera detects the different light intensities of the light reflected by the plane portions and the profiled patterns of the web of corrugated cardboard. This electronic image in the camera is evaluated by an evaluation device for determining the distance of the profiled patterns from each other.