PURPOSE: To enable to draw out ions with high luminance unobtainable by a conventional ion source device even from a low energy ion beam by heightening strength of an electric field.

CONSTITUTION: Ions 4 generated by discharge or the like are accelerated between an acceleration electrode 1 and an electron deterrent electrode 2 and retarded between the electron deterrent electrode 2 and an outlet electrode 3 while being drawn out with the fixed energy. The strength of an electric field between said electron deterrent electrode 2 and the outlet electrode 3 is made to be not less than 6kV/mm. The density of an ion current generated in the ion generation part 5, the potential between the acceleration electrode 1 and the electron deterrent electrode 2 and the distance between the acceleration electrode 1 and the electron deterrent electrode 2 and fixed. Said required strength of the electric field can be obtained by regulating the distance between the electron deterrent electrode 2 and the outlet electrode 3.