To provide a method for performing optimal image correction of each part while visually recognizing the difference among a plurality of images of different color tone easily.

A floating window 70 is displayed at a main display section 41 together with a correction object image 44. The floating window 70 is divided into four display areas 71-74. The same color area of the correction object image 44 as that of a pixel corresponding to a reference point 70a is displayed as a color tone regulation object area at each display area 71-74. Images being displayed at respective display areas 71-74 have different color tones and an operator can select an image at a display area of desirable color tone. When a display area is selected, the part corresponding to the color tone regulation object area of the correction object image 44 is replaced by an image corresponding to the selected display area and the color regulation results are reflected.