To automatically predict an input on an optional position during the input of a character string, to exclude a grammatically invalid predictive candidate, and to present a predictive candidate matching with the context of a document being inputted at present to a user.

A character string inputted from an input part 101 is transferred to a retrieving character string generation part 105, which generates a partial character string group including a final character. The partial character string group is transferred to a predictive dictionary retrieving part 107 as a retrieving character string and the retrieving part 107 retrieves headings of which reading is coincident with the partial character string at the front or completely coincident from a predictive dictionary 108 as a predictive candidate. A context judging part 111 judges a context related to the document being inputted at present and a grammatically valid candidate is selected from the predictive candidates and preferentially presented through an output part 103.