In accordance with alphabet input method information for each user, a word formed of an alphabet string is registered in a word dictionary, in a state where “dotto” being added before each alphabet and one of a set of alphabets difficult to distinguish from each other like “M and N” and “B and P” is repeated twice. For example, a word “PAM” and a feature of time series corresponding to “dotto P P doddo A dotto M” are registered in association with each other. When a user performs a speech input of “PAM”, in accordance with the user's alphabet input method information, the user utters “dotto P P dotto A dotto M”. A speech recognition is performed on this sound data using the word dictionary corresponding to the user's alphabet input method information.