PURPOSE: To perform plotting processing while following up pen input speed on the liquid crystal tablet connected with an information processor.

CONSTITUTION: This device is provided with a graphic memory(GM) 15 for converting pen coordinate information inputted from a tablet 19 to display data and storing them without passing that information through a host computer 4, and a user can select whether a GM 14 for storing the image data from the host computer is used for an image to be displayed on a liquid crystal display panel 16 or this GM 15 is used for it as needed corresponding to a pen input. As a result, by switching an image source selector 18 to the side of the GM 15 at the time of drawing plotting when pen following speed especially gets low, the pen following speed is accelerated, and more natural plotting work is enabled.