PURPOSE: To obtain a method for extending display data in which it is not necessary to use plural frequency clocks without deteriorating a processing speed by installing a circuit for generating the intermediate value of display data in a circuit for driving a dot matrix display device.

CONSTITUTION: A dot matrix display panel is provided with plural signal electrodes (y)0 to (y)5, and plural scanning electrodes crossing those signal electrodes (y)0 to (y)5, and display dots are formed at the crossing positions of the signal electrodes (y)0 to (y)5 and the scanning electrodes. In a driving circuit, display data for one display line are successively shifted in a shift register 30, and impressed to the signal electrodes (y)0 to (y)5. Then, at the time of driving at least one part of display lines, an intermediate value between the display data previously impressed to the signal electrodes (y)0 to (y)5 and display data newly arranging in the shift register 30 is generated, and the generated intermediate value is impressed to the signal electrodes (y)0 to (y)5 so that the display data are extended.