A scanning electron microscope using the retarding method and the boosting method includes a sample holder for holding a sample on the sample holder; a shield electrode arranged between an object lens and the sample, in which an aperture for passing said primary electron beam is formed; a negative-voltage applying circuit for applying a negative voltage to the sample holder and the shield electrode; an acceleration tube located in an electron-beam passing hole in the object lens, provided to pass a primary electron beam, for further accelerating the primary electron beam; and a control electrode located between the acceleration tube and the sample, in which an aperture whose size is smaller than the aperture formed in said shield electrode is provided to pass the primary electron beam, a positive voltage in the positive direction to the negative voltage being applied to the control electrode, superimposed on the negative voltage.