PURPOSE: To obtain a measuring method by which two-dimensional distribution of the quantity of an adsorbed gas can be measured and which is effective for elucidating the gas discharging mechanism or developing a material with low-discharge gas.

CONSTITUTION: The title system only detects a desorbed gas 4 directly entering a vacuum gauge 5 from the surface of a material 1 by desorbing an adsorbed gas by irradiating the absorbed gas with a pulse-like electron beam 3 and synchronizing the measuring timing of the gauge 5 to the irradiation of the beam 3. In addition, the system finds the two-dimensional distribution of the quantity of the gas adsorbed in the surface of the material 1 by scanning the irradiated position with the beam 3.