To make a density of output images proper by correcting a change of an output density characteristic due to a change in output conditions for the images.

A density correction image is formed by an image signal of a predetermined density level. A density of the image is measured by a density- measuring part 131. A density to be measured and a standard density at a corresponding level are compared at a density correction table-forming part 120, thereby to form a density correction table 119 determining a rule to correct a density level of image data so that an output density characteristic shows a linearity. A density-correcting part 118 corrects the density of image data according to the density correction table 119.