PURPOSE: To draw out a metallic ion stably for a long time in order to secure the leading-in of a microwave in the plasma constantly, by preventing the separation of a metal to a microwave incident window generated when the metallic ion is drawn out by a microwave ion source.

CONSTITUTION: The discharge chamber 1 of a microwave ion source is divided into a microwave incident side discharge chamber 12 and an ion beam drawing- out side discharge chamber 13 through a dielectric 11 provided with a plasma passing hole 14. The plasma including no metal is generated in the discharge chamber 12, while the plasma including metals is generated in the discharge chamber 13, and only the plasma including no metal is contacted to a microwave incident window 3.