1. A character recognition apparatus having recognition means for recognizing input character strings and display means for displaying recognized results, said character recognition apparatus comprising: a word dictionary storing word identification information and hierarchy information for layering a plurality of words into a hierarchy and for recognizing each of said words within said hierarchy; a character transition probability table storing at least probabilities of transitions from any one character to another, and those pieces of said word identification information which correspond to combinations of characters resulting from said transitions; optimization means for using said character transition probability table in optimizing candidate character strings obtained by said recognition means; and retrieval means for searching through said word dictionary for words defined by those pieces of said word identification information which correspond to the optimized candidate character string, thereby retrieving the searched words which are identified by the applicable pieces of said hierarchy information and which have yet to be input.