PURPOSE: To realize a function scrolling a picture or dividing the picture by the control of a hardware when no color display and no multilevel display are performed by looking at a using area of a video memory again and securing a video memory space larger than pixels displayable really.

CONSTITUTION: When a monochrome mode is specified, by a display control part 2, the address control of the display data and the switching control of a display mode are performed, and since no leading address of each line becomes address space where the data displaying virtual display space are continued, the address control for reading out the data from a video memory 1 is performed. By a display data control part 3, the read data are segment in bit, '0' is written in a useless bit position to be outputted to a display data conversion part 4, and by the conversion part 4, only the entry used in a moraochrome display in a conversion table used for the color display and the multilevel display is used to be outputted to a display device 5.