To facilitate the adjustment of gray for displaying on a monitor and to print an appropriate image by quantitatively displaying a fixed amount of digital picture element data in the gray component of a standard image fetched with a scanner, on the monitor.

A special negative image corresponding to a prescribed density is stored in an image memory 106, as the standard image, at the time of imposing conditions for the display density of the monitor 104. An image signal processing part 102 is provided with a simulator adjusting part 120 for supporting the adjustment of the visible state of the monitor 104. An arithmetic part 124 calculates the additional average value of the gradation value of each of R, G and B of picture elements extracted by an image extracting part 122. A display instruction part 126 outputs an instruction signal for displaying the calculated additional average value of the gradation value of each of R, G and B, at the fixed position of the monitor 104 in real time and the additional average value of each of R, G and B is quantitatively displayed on the monitor 104 with the instruction signal.