Abstract: The known quality inspection method for printing matter, in which a printed pattern on the printed matter is optically imaged on photo-sensitive elements and the depth of the print of the printed matter is detected by converting intensities of light incident the respective photo-sensitive elements to electrical quantities, is improved. The improvements reside in that from momentarily changing detection signals are obtained by optically scanning the printed matter during its travel, detection signals generated in a particular area are extracted to be used as a reference signal, and anomalies occurring in the printed matter are detected by comparing the momentarily changing detection signals with the reference signal. Preferably, the particular area is an unprintable area, and detection signals generated from a printed area are compared with the reference signal. More preferably, detection signals generated from a non-patterned area are compared with the reference signal.