PURPOSE: To reduce the cost of a device without requiring a complicated hardware by constituting a text screen with a software.

CONSTITUTION: A display control part 1 is activated every fixed time by an interval timer 2 to compare the contents of a virtual text VRAM 8 with the contents of a comparing text VRAM 4 one by one byte. When both values are equal to each other, no operation is executed, but when respective values are different, the data in the VRAM 3 are transferred to the VRAM 4 and a character font corresponding to the text code is read out from a font ROM 5 and developed to a bit map VRAM 6. Consequently, the hardware can be simplified and the cost can be reduced.