A diagnostic system comprises: a spectral imaging means that captures a spectral image within a predetermined wavelength range in a body cavity and obtains spectral image data an image processing means that receives the spectral image data, determines an index value indicating a region that is highly likely to be a lesion from the spectral image data, and generates and outputs an extracted lesion image based on the index value and a monitor on which the extracted lesion image is displayed. The image processing means performs multiple regression analysis for each pixel of the spectral image with the spectral image data as a dependent variable and respective light absorption properties of oxyhemoglobin and deoxyhemoglobin as independent variables, and determines the index value based on respective concentrations of the oxyhemoglobin and the deoxyhemoglobin.
