PURPOSE: To provide an image memory controller capable of outputting an image with excellent gradient at a high speed with the same software without changing the method of memory access even when the number of gradation to be displayed is changed at every pixel in an output device.

CONSTITUTION: The image memory controller is constituted of a first image data storage means 10 transiently storing first image data written in an image memory 4, a first write address storage means 11 transiently storing a first write address in the image memory 4, a second image data storage means 12 transiently storing second image data written in the image memory 4, a counter 13 generating a second write address according to the first write address, a shift register 14 shifting the first image data synchronizing with the counter 13 and a write pulse generation means 15 generating a write pulse writing the second image data in the image memory 4 by the output of the shift register 14.