An image processing device, comprising an obtaining means that obtains color endoscopic image data, a color space conversion means that converts a color space of the color endoscopic image data to an HSI color space based on hue, saturation and intensity or an HSV color space based hue, saturation and a value, a lesion pixel judgment means that judges, for each of pixels constituting a color endoscopic image, whether or not each pixel is a lesion portion based on the hue and the saturation, an overlay processing means that executes an overlay process which changes a color of the pixel judged to be the lesion portion by the lesion pixel judgment means, and an overlay image display means that displays an overlay image obtained by subjecting the color endoscopic image to the overlay process.
