Abstract: In an ion source, within a support body which supports a plasma production chamber for producing a plasma on the basis of an ion source flange, a cavity is provided ranging from a position near the plasma production chamber to a position near the ion source flange. The cavity serves as a cooling medium passage which introduces a cooling medium to a position near the plasma production chamber to cool the plasma production chamber. The plasma production chamber is cooled at a position very near it by the cooling medium. Therefore, temperature of the plasma production chamber at the time of plasma production is kept at low temperatures.