1. A method for creating a speech recognition dictionary to be used for creating a mail through voice input in an application, the method comprising the steps of: receiving a transmitted mail from a transmission source; obtaining a speech recognition dictionary corresponding to the transmission source, wherein the speech recognition dictionary is obtained from a memory which retains a plurality of speech recognition dictionaries; detecting if a mail creation processing involving the transmitted mail is started; reading the transmitted mail when the mail creation processing is detected; analyzing the transmitted mail and extracting a plurality of unknown words; updating the speech recognition dictionary by adding thereto the plurality of unknown words; storing registration time information for each of the plurality of unknown words, which indicates a time when the unknown word is added to the speech recognition dictionary; and deleting each one of the plurality of unknown words when a specified period of time set for the each one of the plurality of unknown words has elapsed from the time indicated by the registration time information.