To automatically insert a punctuation mark into a natural flow of dictation by discriminating a predetermined specific character string from character strings recognized according to an inputted speech and adding one punctuation mark.

When speech input is started (S2), a KANA(Japanese syllabary) character string is discriminated (S3) corresponding to the progress of speech. A clause structure is analyzed from the KANA character string (S4) and KANJI (Chiniese character) automatic conversion is performed by clauses (S5). Then the necessity of punctuation mark addition is analyzed from the character string recognized according to the inputted speech and a punctuation mark is automatically added (S6). In concrete, it is decided that the ending of a clause is a predetermined specific character or character string and one punctuation mark is added. Then it is confirmed whether or not the speech input ends (S7). Consequently, even when the speech input of a document is performed along a natural flow of dictation at the time of the creation of the document, the document is punctuated properly with punctuation marks to facilitate corrections after the speech input.