According to an aspect of disclosed embodiments, a computed tomography (CT) image processing apparatus includes: an image processor configured to set two or more CT number ranges of interest defined by a window level and a window width for CT numbers of CT image data, and map the CT numbers to display grayscale values of a display; and the display configured to display the CT image data according to a mapping result, wherein a gradient of a graph showing a relationship between the CT numbers and the display grayscale values in a CT number range included in the two or more CT number ranges of interest is greater than a gradient in a CT number range not included in the two or more CT number ranges of interest, wherein the graph showing the relationship between the CT numbers and the display grayscale values has a zero or positive gradient over an entire section, or has a zero or negative gradient over the entire section.