To provide a confidential sheet with a separating mechanism for paper sheets which has eliminated a weak point of a perforation being easily separated at opening a confidential postcard or sheet capable of forming an envelope.

A particle of a rubber or rubber composition is applied on the overlap width of a sheet 11 for forming a postcard or envelope and on the perforated cutting line 111 sections for opening. The applied particle is dried, then a seal adhesive layer 113 without tackiness is formed. The seal adhesive layer 113 can couple the seal adhesive layers each other with peelability by folding the sheet, superposing the overlap width and rubbing the opposite side of the width. By forming the adhesive layer 113 on the sections of the perforated cutting line 111 for opening, the cutting separation of the perforation is reinforced at separating/opening from the perforation at the time of opening the confidential sheet.