To provide a secondary ion mass spectrometer capable of changing the incident angle of primary ions with respect to a sample without changing a desired detection condition between the sample and a detector.

This secondary ion mass spectrometer includes this irradiation direction-variable ion irradiation device, a sample base, and a mass spectrograph. The irradiation direction-variable ion irradiation device has a mechanism which includes: a fixed ion gun; a first deflection plate capable of controlling the change of the traveling direction of emitted ions, and nearer to the ion gun in an irradiation path; and a second deflection plate capable of controlling the change of the traveling direction of emitted ions, and farther from the ion gun, and in which the first deflection plate and the second deflection plate can rotate independently of each other around a certain point.

COPYRIGHT: (C)2008,JPO&INPIT