1. A character string recognition apparatus, comprising: a key character code extraction unit automatically extracting a code string of a key word which is a node of a character string from a character string category to be recognized and expressed as a character code; a key word extraction unit extracting a key word extracted by said key character code extraction unit or a part of the key word is extracted from a character string image; and a recognition unit holistically recognizing character strings in partial areas determined by the extracted key words.