Electron scanning microscope and image generation method

A scanning electron microscope which irradiates, with an electron beam, a specimen placed in a space of an atmospheric pressure atmosphere and thereby acquires an image of the specimen on the basis of a signal generated from the specimen, the scanning electron microscope comprising:

• an electron optical lens barrel which includes an electron source and irradiates the specimen with a primary electron beam;
• a chassis which is directly bonded to an inside of the electron optical lens barrel and has an inside turning into a lower vacuum state than the inside of the electron optical lens barrel at least during the irradiation with the primary electron beam;
• and
• an isolation film which isolates the space of the atmospheric pressure atmosphere where the specimen is placed and the inside of the chassis, from each other, and transmits the primary electron beam;
• contamination on the isolation film is decomposed by irradiating the isolation film with the primary electron beam;
• an orifice which holds an air pressure inside the electron optical lens barrel below an air pressure inside the chassis, directly below the electron optical lens barrel.