PURPOSE: To stably introduce a constant amount of analysis sample ions independent of the passage of time from high frequency inductively coupled plasma(ICP) to a magnetic field type mass spectrograph(MS) by preventing etching of a suction opening of a sampling cone caused by discharge of inductively coupled plasma.

CONSTITUTION: An ion induction device 20 combines a high frequency inductively coupled ion source with a mass spectrograph 10, and introduces ions 3 through a suction opening A which is differentially evacuated. An electrode 12 which is kept at specified voltage 13 against acceleration voltage 11 is arranged on the front side or the rear side of the suction opening A, and its tip is inserted into inductively coupled plasma 3 which is not yet sucked or was already sucked to prevent discharge producing between the inductively coupled plasma 3 and the suction opening A.