PURPOSE: To make it possible to analyze a thin film with a high sensitivity, by irradiating a primary ion beam to a sample and by energy-analyzing back secondary ions emitted from the reverse face of the irradiation point and by performing mass analysis.

CONSTITUTION: Primary ions from PIG ion source 1 scan sample surface 5 due to leading-out electrode 2, Einzellens 3 and deflecting electrode 4, and the primary ion quantity passing through sample 5 is monitored by Faraday cage 6. Secondary ions generated from the back face of sample 5 are sent to mask filter 8 by spherical energy analyzer 7, and mass separation of generated secondary ions is performed.