To provide paper for preparing an envelope which prevents stealing of personal information by that the envelope is sent to an address different from the original one due to alteration of the address or to replacement of the envelope by some different one showing the different address.

The paper 11 for preparing the envelope having the address concealed has a constitution wherein an envelope top paper part 12, an envelope bottom paper part 13 and a sealing part 14 are connected through the intermediary of folding parts X1 and Y, while the address is expressed beforehand on the surface side of the envelope top paper part 12, and gluing part for applying an adhesive is provided on the back sides of either the top paper part 12 or the bottom paper part 13 and of the sealing part 14. A binding piece 21 and an auxiliary piece 22 are connected to the opposite ends of the paper 11 for preparing the envelope, through the intermediary of cutting perforations 19 and 20 parallel to the folding parts X1 and Y. The paper 11 is folded back at the folding part Y, with the address expressing surface of the envelope top paper part 12 put inside, and the binding piece 21 is bound to the auxiliary piece 22 with the adhesive 23.