PURPOSE: To reduce the amount of loss of ions to be measured between an extraction electrode and an ion lens by storing a gate valve in a fore chamber and by shortening the distance between the extraction electrode and the ion lens.

CONSTITUTION: Ions generated by ionizing a sample by a high frequency induction coupled plasma 7 pass through a nozzle 8 and a skimmer 9, and are converged passing from an extraction electrode 14a, through an opened gate valve 21, an ion lens 14b, to a quadrupole lens 14c, and are introduced into a quadrupole mass filter 16. The ions guided to high vacuum by the electrode 14a are converged while a condition of small amount of loss of ions to be measured between the electrode 14a and the lens 14b, is maintained, since the distance between the electrode 14a and the lens 14b is short, and the ions are introduced into the mass filter 16. A high frequency induction coupled plasma mass spectrometer of high sensitivity and stable operation can thus be achieved.