PURPOSE: To make it possible to view address information of an insert in an envelope by a method wherein an address entry column is formed on a fold line and the address is viewable through a window when a sheet of paper is folded.

CONSTITUTION: A right side region of a sheet of paper is first folded back on a left side region along a foldline 26. Further, when aforesaid sheet is folded along a foldline 82, a first address entry portion becomes a position corresponding to a window 56 and a return envelope is prepared for sending. An insert 83 is held by a foldline 82 and it is thus possible to confirm the address through the window 56 by stopping the address entry portion 58 to be moved after a folding process around the foldline 82. A receiver of an envelope tears the envelope to be opened along perforations 28, 76 and 80. The return envelope is separated from the remaining envelopes along the foldline 26. Next, an insert 83 is inserted in the return envelope as required and a protective piece 32 is removed, an adhesive belt 34 for being used as a reusable lid flap being folded back. This completes the process for returning an envelope.