To realize sending of a card type CD-ROM by a sealed letter, in which unsealing can be properly done at an unsealing perforation, by a method wherein no breakage of the perforation develops even at the bumping of the sealed letter, which is equipped with the unsealing perforation and folding perforations and in which a card-like article is sealed, against the wall surface or the like of a mail sorting machine during a sorting treatment with the mail sorting machine.

In the side part unsealing perforation 8 and the sealed piece unsealing perforation 9 of one envelope-forming paper piece 5, in which a card- like article housing part 11 is located, the sum of the length of one tie and that of one cut is set to be 2 to 4 mm and the ratio of the length of the tie to that of the cut is set to be within the range of 0.4 to 0.6. On the other hand, in the folding perforation 7, the sum of the length of one tie and that of one cut is set to be 2 to 4 mm and the ratio of the length of the tie to that of the cut is set to be within the range of 0.7 to 1.5.