PURPOSE: To analyze gas component trapped in the local region such as the crystal boundary or flaw of a solid material.

CONSTITUTION: A sample 4 is placed on a sample placing stand provided in a vacuum container 2 and a probe 6 of scanning tunneling microscope having a heating means 7 is arranged in opposed relation to the sample 4. The scanning electron microscope image of the sample 4 displayed on a CRT 16 is looked to determine the observation visual field of a scanning tunneling microscope and the image by the scanning tunneling microscope is observed on a CRT 11. The probe 6 is allowed to approach the place to be analyzed on the sample on the basis of the image on the CRT 11 and the probe 6 is heated by the heating means 7 to selectively heat only the local region of the sample 4. The gas separated from the local region of the sample by heating is detected and analyzed by a mass analyser 19.