PURPOSE: To prevent detection sensitivity lowering at the time of analysis by providing a controller making a gas flow rate at the time of analysis smaller by a fixed value α than that at the time of sensitivity adjustment.

CONSTITUTION: The adjustment of detection sensitivity is made so as to make the signal strength of an argon dimer become maximum. After such a sensitivity adjustment is finished, the analysis of a specimen is made at a gas flow rate B smaller than that A used in the sensitivity adjustment. Here the relation, B=A-α, exists between the gas flow rates A and B, and the value of α is previously determined from data obtained by experiments, etc., to be memorized in a memory within a controller 21. Thereupon a gas flow rate supplied to ICP-MS is made the same flow rate A as at the time of sensitivity adjustment. Consequently the maximum signal can be obtained when a specimen is vaporized in a heat vaporization induction device, and sensitivity lowering can be prevented.