Provides subtitle generation methods and apparatus which recognizes voice in a presentation to generate subtitles thereof, and retrieval apparatus for retrieving character strings by use of the subtitles. An apparatus of the present invention includes: a extraction unit for extracting text from presentation documents; an analysis unit for morphologically analyzing text to decompose it into words; a generation unit for generating common keywords by assigning weights to words; a registration unit for adding common keywords to a voice recognition dictionary; a recognition unit for recognizing voice in a presentation; a record unit for recording the correspondence between page and time by detecting page switching events; a regeneration unit for regenerating common keywords by further referring to the correspondence between page and time; a control unit for controlling the display of subtitles, common keywords, text and master subtitles; and a note generation unit for generating speaker notes from subtitles.