PURPOSE: To print a mark such as bar code on an opaque or semi-opaque label which is affixed on mails, and clearly impart the bar code on mails.

CONSTITUTION: By inputting with keys information such as zip codes being put on a postcard 2, the input information is converted into a bar code and imparted to the postcard. For such a coding device, a label paper 29 for which a semi-opaque label is affixed on a support paper 40 is fed out from a label paper reel 28, and the bar code is visibly printed with a fluorescent ink on the label of the label paper by a thermal head unit 33. Then, the label for which the printing is completed is separated from the support paper by a label separating machine 38, and carried to an affixing roller 41 and pressing roller 42, and the label is affixed to a specified location of the postcard by the affixing roller and pressing roller.