There is disclosed a low-vacuum scanning electron microscope wherein a bias voltage is applied to a specimen. A primary electron beam is made to strike the specimen, producing secondary electrons which are accelerated by an electric field producing an electron avalanche effect. Positive ions traveling toward the specimen reach the specimen or specimen holder. Then, the electrons lose their electric charge and return to molecules. In this way, a scanned image corresponding to a secondary electron image can be obtained based on the specimen current.
