PURPOSE: To prevent charge of the surface of a measuring object by supplying inert gas ion of low energy to the surface of the measuring object.

CONSTITUTION: In a surface analytical method, a charged ionized inert gas is flowed into the surface of a charged measuring object in parallel with the surface or at a fine angle of incidence with low energy. In other words, in case the surface of a measuring object is negatively charged, when a positive ion of positively ionized inert gas passes on the surface of the measuring object, the positive ion takes away the negative charge on the surface of the measuring object to be neutralized and becomes a neutral atom. Reversely, when the surface of the measuring object is positively charged, negatively ionized inert gas is made to flow on the surface of the measuring object. It is thereby possible to prevent simply and certainly the surface of the measuring object from being charged, so that an accurate spectrum can be obtained.