PURPOSE: To constantly learn a correct word by providing with a learning word deciding means by erasing a word with erroneous reading or that with an erroneous word boundary from a learning word and adding a word with a correct reading and word boundary.

CONSTITUTION: The learning word deciding means decides a learning word by comparing a learning word which is the output of a preferential order deciding circuit 3 with a word divided by a word dividing circuit 7. A learning word deciding circuit 8 compares a most preferential word included in the learning word with the divided word and when both of the reading and the word boundary are coincided, the learning word deciding circuit 8 outputs them to a learning word storing part as they are. Then, the reading is different, words including at least one character of a reading character string corresponding to the different part in its character string are all erased from the learning words and the divided words are added to the learning words as the most preferential words in stead. on the other hand, when the word border is different, the most preferential word is changed so as to make the most preferential word lower than the divided word.