1. A word string collating apparatus for collating an input word string and words in a word dictionary when a partial word string is extracted from the result of character recognition for a word string including a plurality of words, comprising: correspondence setting means for variously setting correspondence relations between the words of the input word string and the words in the word dictionary according to the number of words of the extracted partial word string; deriving means for deriving each distance between the words which are set into the correspondence relation by said correspondence setting means based on each similarity between the words and deriving the positional relation of each word of the input word string which is set into the correspondence relation by said correspondence setting means; and determining means for deriving an evaluated value based on the positional relation derived by said deriving means and the distance between the words which are set into the correspondence relation by said correspondence setting means for each type of the correspondence relation set by said correspondence setting means and determining a partial word string extracted from the input word string based on the evaluated value.