PURPOSE: To perform the highly sensitive analysis of gas and to make it possible to diagnose the abnormality in the inside of an electric apparatus by once adsorbing the gas having the abnormal component with a gas adsorbent in a gas-adsorbent containing case, thereafter heating the containing case, and desorbing the gas.

CONSTITUTION: A gas sampling valve 11 is provided at the outlet of a gas adsorbent containing case 7 containing a gas adsorbent 9. A sample-gas sampling bag 12 which is evacuated beforehand is connected. The direction of the valve 11 is changed, and the gas is made to flow into the case 7. At the same time, the case 7 is heated with a heater 14. Then, the gas which flows into the case 7 is once adsorbed with the adsorbent 9. Thereafter, the gas is heated and desorbed. After the specified time, the direction of the valve 11 is changed, and the gas is sampled into the sampling bag 12. Then, the sampled gas 13 is analyzed by gas-chromatography. Since a large amount of the gas can be made to flow into the case 7 in this way, the adsorbent 9 adsorbs the large amount of the gas having the abnormal component. In this way, the highly sensitive analysis is performed for the gas having the very minute amount of the abnormal component, and the abnormality in the inside of the electric apparatus such as a transformer can be diagnosed.