To secure an large area of information surface and to make a set with a postcard surely by a method in which a sheet is folded to obtain a letter, a wide area can be obtained by unfolding the sheet after opening, and a postcard for a reply is integrated with the sheet.

A sheet main body 2, after being folded in the longitudinal direction of a postcard, is made to be folded rollingly in the cross direction of the postcard, a sealing part 7 is formed over the upper end fringe of the main body 2, an adhesion part 10 which is bonded peelably to the opposite place of the middle folded part is formed, a seal part 12 which is bonded to the lower paper of an envelop when the sheet is folded rollingly is contacted connectingly with the upper paper of the envelop in a letter, and a postcard sheet 15 is attached to one surface which is to be an inner side when folded rollingly in the sheet surface.