PROBLEM TO BE SOLVED: To solve the problems such as a difficulty in accurately removing a surface reflection component of a highlight part and the like, a high calculation cost, and a disadvantage in reducing a diameter of the tip of an electronic scope.SOLUTION: An image signal generating device includes: means for extracting a first color signal corresponding to a first wavelength region and a second color signal corresponding to a second wavelength region from image signals of a biological tissue irradiated with the irradiation light having a plurality of wavelength regions including first and second wavelength regions whose absorption properties in the biological tissue are different； means for calculating a pixel value approximate distribution approximate to the pixel value distribution of the second color signal based on the pixel value distribution of the first color signal； means for generating an image signal of a surface reflection component of the biological tissue based on a difference between the pixel value approximate distribution of the second color signal and the pixel value distribution of the second color signal； and means for generating an image signal of an internal reflection component of the biological tissue by subtracting the image signal of the surface reflection component from the image signal of the biological tissue.SELECTED DRAWING: Figure 2
