PURPOSE: To improve the printing speed by improving the reclamation rate of a generated dot pattern.

CONSTITUTION: When a generated dot pattern for a font is stored in a font cash memory (it is referred to as 'font cash' hereinafter) 18, the existence/ absence of a space area in the font cash 18 is judged, and when there is no space area, the dot pattern of a specified font is transferred from the font cash 18 to a dot pattern compression unit 20 and then, deleted, and the dot pattern which should be stored is stored by a printer control unit 12. By this method, even when a space area is used up, a newly generated dot pattern can be stored in the font cash 18. In the meantime, the deleted dot pattern is compressed by the dot pattern compression unit 20, and then is stored in a compressed data storage unit 22. Therefore, even characters which are deleted from the font case 18 can be reclaimed.