An image processing device characterized by comprising: an image signal inputting unit for inputting image signals of three colors including at least one narrowband image signal; a signal ratio calculator for calculating a first signal ratio between the image signals of predetermined two colors and a second signal ratio between the image signals of two colors different from the first signal ratio, based on the image signals of three colors; a color difference enhancer for performing an expansion process, the expansion process expanding a difference between first and second signal ratios in a first area and first and second signal ratios in a specific area, the first area being located in a two-dimensional space formed by the first signal ratio and the second signal ratio, and the specific area being located in an area different from the first area in the two-dimensional space, wherein the first area is an area where the first and second signal ratios are maintained unchanged in the first expansion process, and wherein the first and second signal ratios in the specific area are processed to expand the difference from the first and second signal ratios in the first area in the expansion process, the first area containing first and second signal ratios corresponding to normal mucosa on an object of interest and the specific area containing first and second signal ratios corresponding to an abnormal region on the object of interest; and a display unit for displaying an image in which a color difference between the normal mucosa and the abnormal region is enhanced based on the first and second signal ratios subjected to the expansion process, the difference in reflection density between the normal mucosa and the abnormal region being greater than in a case where all of the image signals of three colors are broadband image signals, and the color difference being displayed greater than a color difference in the case where all of the image signals of three colors are the broadband image signals. an image signal inputting unit for inputting image signals of three colors including at least one narrowband image signal; a signal ratio calculator for calculating a first signal ratio between the image signals of predetermined two colors and a second signal ratio between the image signals of two colors different from the first signal ratio, based on the image signals of three colors; a color difference enhancer for performing an expansion process, the expansion process expanding a difference between first and second signal ratios in a first area and first and second signal ratios in a specific area, the first area being located in a two-dimensional space formed by the first signal ratio and the second signal ratio, and the specific area being located in an area different from the first area in the two-dimensional space, wherein the first area is an area where the first and second signal ratios are maintained unchanged in the first expansion process, and wherein the first and second signal ratios in the specific area are processed to expand the difference from the first and second signal ratios in the first area in the expansion process, the first area containing first and second signal ratios corresponding to normal mucosa on an object of interest and the specific area containing first and second signal ratios corresponding to an abnormal region on the object of interest; and a display unit for displaying an image in which a color difference between the normal mucosa and the abnormal region is enhanced based on the first and second signal ratios subjected to the expansion process, the difference in reflection density between the normal mucosa and the abnormal region being greater than in a case where all of the image signals of three colors are broadband image signals, and the color difference being displayed greater than a color difference in the case where all of the image signals of three colors are the broadband image signals.