To provide an encoding method and a decoding method for embedded information of an electronic document which can embedded or extract information such as signature information to/from an electronic document.

When a signature data 3 are embedded in a Japanese-language document 1 of digital data where punctuation marks consist of full size characters and (half size characters)+(half size spaces), the signature data 3 is converted into binary data by a character string/binary data conversion means 4, the code of the signature data 3 converted into the binary data is assigned to the punctuation marks consisting of full size characters and (half size characters)+(half size spaces) by an assignment means 5 and the assigned code is embedded in the Japanese-language document 1 by an embedding means to prepare a signed document 7.