PURPOSE: To process by detecting what were not detectable so far surely, by detecting an express mark stamped on an express mail, even on the express mail on which an undetectable postage stamp is stuck.

CONSTITUTION: A lighting lamp 7 irradiates an express mark on an express mail and its reflecting light is resolved of wavelength by a photoelectric converter 8. A hue signal of the express mark 2 is extracted and outputted at a hue discriminating circuit 9 from an electric signal which was photoelectrically converted. This hue signal is transported to an area detecting circuit 10 in order to discriminate from letters and designs having the same color, and it is detected that the area of the mark 2 is above a prescribed value. While, as a detecting signal is transported to a field circuit 13 in accordance with transportation of mails 1 by a light source 11 and a photocell 12, a field signal which is suitable for a field a is outputted from the field circuit 13 and is inputted to an inputting terminal (b) of the above-mentioned AND circuit 14. As an AND is, thereat, brought into existence between an outputting signal from the above-mentioned circuit 10 and the field signal from the above-mentioned circuit 13, an AND circuit 14 is outputted as an express mark signal, i.e. an express mail signal.