PURPOSE: To allow the simple analyzing operation and the high-sensitivity detection of each sample by guiding each sample developed into a thin layer directly into a detecting device adjacent to a developing tank and performing the qualitative analysis by the mass spectrometry.

CONSTITUTION: A thin layer 1 mounted with a sample is fitted to a thin layer holder 11, the lower section of the thin layer 1 is immersed in a developing solvent 12 by a driving device 9 to develop the sample. The developing solvent 12 is then discharged, the whole device is made vacuum by a vacuum pump, Ar gas is fed to an RF discharge chamber 19, high frequencies are applied to an RF coil 3 and the holder 11 to form RF plasma in the discharge chamber 19. The negative ions thus charged pass an electrode 2 and accelerated by an accelerating electrode 4 and fed to a mass spectrometer 6. The mass- separated ions are detected by an ion detecting device 7. The thin layer 1 is then moved upward by the device 9, and the next portion is analyzed. The simple analysis can be performed by the operation with such structure.