PROBLEM TO BE SOLVED: To provide ICP-MS method and apparatus which can calibrate a magnetic field intensity without using a standard sample including the same ion as a target ion to be measured when the MS field intensity is to be calibrated to execute a high-resolution SIM measurement. SOLUTION: The ICP-MS method comprises a preparatory measurement for determining a signal position of the target ion and a real measurement in which the high-resolution SIM measurement is carried out with an apparatus condition being set based on information on the determined signal position of the target ion so that the target ion is selectively detected. The preparatory measurement includes a process of measuring a mass spectrum of interfering ions of a known precision mass number present in a plasma, a process of specifying a peak position of the mass spectrum of the interfering ions and a process of determining on the basis of the specified position and the precision mass number the position where the signal of the target ion appears. The interfering ions are NH+, CO+, NO+, ArH+, ArC+, ArN+, ArO+, ArCl+, Ar2+, etc.
