A plasma ion source includes: a gas introduction chamber, into which raw gas is introduced; a plasma generation chamber connected to the gas introduction chamber and made of a dielectric material; a coil wound along an outer circumference of the plasma generation chamber and to which high-frequency power is applied; an envelope surrounding the gas introduction chamber, the plasma generation chamber and the coil; and insulating liquid filled inside the gas introduction chamber, the plasma generation chamber and the envelope to immerse the coil and having an dielectric strength voltage relatively greater than that of the envelope and the same dielectric dissipation factor as the plasma generation chamber.