To achieve miniaturization and making low cost of an apparatus by simplifying a constitution while profitability and a wide use property at the time of preparing a sealed letter are significantly raised.

An apparatus for automatically preparing a sealed letter is equipped with a paper feed part 2 wherein large sized envelope paper Pe and small sized document paper Pd... are selectively fed, an adhesive application part 3 wherein an adhesive J is applied at a preliminarily set position to the envelope paper Pe sent from the paper feed part 2, and a paper folding part 4 wherein one sheet of the envelope paper Pe sent form the adhesive application part 3 is positioned at a first set position, one sheet or at least two sheets of document paper Pd... sent from the paper feed part 2 are positioned at a second set position on the envelope paper Pe at the first set position, and the envelope paper Pe is stuck by folding successively a first fold part and a second fold part which are divided into three parts longitudinally.