PURPOSE: To automatically decide the layer of a character by using the size of the character for each character string.

CONSTITUTION: The segmentation of the character string and character segmenting processing are performed in steps ST1 and ST2. In each step, processing successively proceeds after the preceding processing is finished. Next, in a step ST3, character layer deciding processing is performed to the segmented character string and character. At the character layer deciding processing of this step ST3, the first character string sequentially arranged in a step ST21 is extracted. Next, it is investigated in a step S22 whether there is any un-processed character string or not and when such a character string does not exist, processing is finished. In the step ST23, the size detection/ character layer decision of a representative character in the extracted character string is processed for calculating the optimum size of the character layer.