PURPOSE: To obtain an image processing unit in which causes to deterioration in image quality being production of a stripe pattern and occurrence of a round- off error being contradicted caused can be suppressed when multi-value processing is conducted through the use of the error spread method.

CONSTITUTION: A control section 23 selects a prescribed error matrix whose spread coefficient differs from a 1st storage section corresponding to a multi- value processing number based on a designation mode set by an operation section 10. Then a prescribed multi-value processing number and an error spread matrix are combined so as to hardly cause a stripe pattern and a round-off error through the error spread operation by a multiplier 24 and the multi-value processing and then balanced thereby preventing the production of them.