Marking method and resecting method

A marking method comprising:

• inserting an endoscope into a subject;
• irradiating, with first light from the endoscope, an observation target site in the subject without spraying a coloring agent into the subject;
• picking up an image of, through the endoscope, second light generated at the observation target site through irradiation of the observation target site with the first light;
• displaying an image in which a site suspected to be a tumor is highlighted by highlight processing which generates the image based on the second light received through the endoscope;
• and
• providing a guide for a range suspected to be a tumor by providing a tissue denatured portion, the tissue denatured portion being provided by denaturing a tissue into a point, dotted-line, or line, around the site suspected to be a tumor by using an energy radiation device while observing the image in which the site suspected to be a tumor is highlighted wherein the tissue denatured portion is provided by flowing a high-frequency current to the subject through coagulation of protein by evaporating a fluid in cells of the tissue.