PURPOSE: To incorporate more information in a sealed letter by a method wherein a wide printing information recording surface which is not divided by a sealing part is formed on three paper pieces connecting to each other through folding perforation lines.

CONSTITUTION: Edges of paper pieces 5, 6 disposed on the both sides of a paper piece 4 disposed on the center are each shorther in length than that of the paper piece 4 in a connecting direction A orthogonal to folding perforation lines 2, 3. The edge of the paper piece 6 which is one of the paper pieces 5, 6 disposed on the both sides is shorther in length than that of the other paper piece 5 in the connecting direction A. The paper piece 5 having the second longest edge in the connecting direction A is folded on the center paper piece 4. The paper piece 6 having the shortest edge is folded thereon. Sealing parts 7 are provided by applying an adhesive to the edges in the connecting direction which are opposed to each other in the folded state. Sealing parts 8 of a weak adhesive power are provided on an edge opposite to the folding perforation line 2 in the paper piece 6 having the shortest edge in the connecting direction and on the surface of the paper piece 5 at a position opposed to the edge.