A structure for enabling control of the plasma potential of an ICP-MS. The structure includes: a shield plate 10 made of metal inserted between a plasma torch 1 and a high-frequency coil 2, a variable capacitor 11 connected between the shield plate 10 and ground, and an insulation member 15 is arranged to prevent contact of the high-frequency coil 2 with the shield plate 10. Even if a sample is introduced into ICP by any known method, it becomes capable to perform ICP-MS analysis while optimizing the response to interfering ions and detection sensitivity.
