PURPOSE: To keep the electron beam radiation quantity constant even if the exciting current and accelerating voltage of an objective lens are changed by changing the lens strength of a focusing lens in response to the change of the lens strength of the objective lens or the change of the feed voltage to a high- voltage section.

CONSTITUTION: An electron beam from an electron gun is focused by the first and second focusing lenses 2, 3 and radiates a sample 5 via the first objective lens 4. The sample 5 is placed near the second objective lens 6, and an expanded image is projected on a projection plane 9 via an intermediate lens 4 and a projecting lens 8. On the other hand, when the focusing is performed by changing the accelerating voltage after conditions are set by the photographing mode, the signal in response to the voltage change V is applied to an amplifier 15 via a control circuit 11, thereby the focusing lens 2 or 3 is controlled to keep the brightness constant. When the exciting current of the objective lenses 4, 6 is changed, the signal V' in response to the exciting current change from a control circuit 13 is applied to the amplifying circuit 15 to keep the brightness constant.