A structure of an electron beam apparatus having shielding properties for shielding against an environmental magnetic field is provided. The electron beam apparatus comprises a mirror barrel for housing a magnetic lens for converging an electron beam onto a specimen and a specimen chamber for housing the specimen, wherein a non-magnetic material having conductivity is used as a material for at least one of the mirror barrel and a main body of the specimen chamber. The material for the mirror barrel or the main body of the specimen chamber is an aluminum alloy and a thickness of a sidewall of the mirror barrel or the main body of the specimen chamber is 10 mm or more. A magnetic plate having a thickness smaller than that of the sidewall of the mirror barrel or the main body of the specimen chamber is provided on an inner sidewall of the mirror barrel or the main body of the specimen chamber.