PURPOSE: To perform resolution conversion with a small amount of hardware at a high speed with respect to the resolution conversion required when a display memory differ from the resolution of the display is used.

CONSTITUTION: A display memory 1 with m1×n1 dots is scanned in an X direction synchronously with a clock signal 302 of a frequency f1. The data, which are read from the memory 1 by the scanning, are latched to a register 4 by the clock signal 302. The output of the register 4 is latched to a register 5 by a clock signal 303 of a frequency f2 (f2/f1=m2/m1), and is converted to the X direction resolution of a display 2 with m2×n2 dots. At a read address preparing circuit 31, a Y address with a decimal section is prepared and the integer portion of the address is used as Y address 306 in a read address 304. The Y address with a decimal section is added with an increment n1/n2 at every X direction scanning and updated. Thus, the Y direction of the memory 1 is converted to the Y direction resolution of the display 2.