An image processing device 3 calculates a three-dimensional shape and feature value information of a curved face of the three-dimensional shape utilizing luminance information from an R-component image of an endoscopic image that is picked up by an endoscope 6. In the image processing device 3, a region having a color tone change of reddening or discoloration is detected based on both R- and G-image components. The value of a detection standard as a threshold value when detecting a polyp as an elevated lesion from an elevation change region on the curved face of the three-dimensional shape is changed depending on the results of the above-described detection. Thus, a polyp can be detected with high accuracy.
