PURPOSE: To detect the constituents desorbed from a sample by heating at high sensitivity.

CONSTITUTION: A sample is heated by a heat source 1 in a vacuum container 5, and molecules and atoms desorbed from the sample are measured by a mass spectrograph 2. The heat source 1 is installed above or obliquely at the front apart from the sample 3, and the mass spectrograph is installed obliquely at the front other than on the diagonal line of the heat source 1 near to the sample 3.