PURPOSE: To obtain a mail form which makes it possible to enclose a reply card in connection and to send an arbitrary amount of confidential information in a concealed state.

CONSTITUTION: In a mail form 10 wherein a plurality of slip pieces are connected through the intermediary of a folding perforation, folded in opposite directions alternately at the folding perforation, pressed and made to adhere to each other to be sealed, cutoff parts H of a postcard size are provided in two prescribed slip pieces to be opposed to each other by folding at the folding perforation, respectively, at positions being symmetric with respect to the folding perforation m4, and adhesive parts 3b' and 4b' are provided on two surfaces to which the cutoff parts H are opposed.