An image processing system includes: a light source portion configured to emit illuminating light to be radiated to an object; a light receiving optical member for guiding return light from the object: a light detecting portion configured to receive the return light caused to be incident through the light receiving optical member to generate an electric signal, amplify the generated electric signal, convert the amplified electric signal to a digital signal and output the digital signal; an image processing portion configured to generate an image based on the digital signal outputted from the light detecting portion and perform gain adjustment for the generated image; and a parameter adjusting portion configured to adjust a predetermined parameter based on a variable range of an output value of the light source portion and a variable range of a gain value in the gain adjustment.