Abstract: A method of forming an image of detailed cilium wrapped by mucus which exists in the epithelial layer of a cellular structure of a bronchus, where the method includes the steps of: irradiating an illumination light to the epithelial layer; generating Fresnel reflected light; irradiating the Fresnel reflected light to an image pick-up optical system; enlarging the Fresnel reflected light by the image pick-up optical system so that the enlarged Fresnel reflected light can be received by the image pick-up element; scanning at a velocity which is more than the velocity of motion of the cilium by the image pick-up element; transmitting image information from the image pick-up element to an observable medium with the naked eye; and displaying the image of detailed cilium by the observable medium.