Abstract: Conventionally, there is a method where a certification of contents is mailed in order to legally prove that intention of one party is transferred to an opposite party. Namely, one party who desires to retain a legal evidence showing that the one party transferred his intention to the opponent party mails the content certification to prove such a transfer of the intention from the one party to the opponent party. However, this method has a problem in that an emotional trouble may arise between the two parties.