PURPOSE: To efficiently remove the charged particles in an atomic beam with small input power by constituting a removing electrode of ≥2 stages and impressing higher negative voltage to a succeeding stage removing electrode than that of a preceding stage removing electrode.

CONSTITUTION: More than two stages electrodes 1 and 2 are composed of the removing electrode which moves charged particles from the atomic beam containing the charged particles. And the succeeding stage removing electrode 2 is impressed higher negative voltage than that of the preceding stage removing electrode 1. The charged particles 4 are pulled-in to the removing electrodes 1 and 2 impressed negative voltage, and plasma is diminished in the removing electrodes 1 and 2. On the other hand, the atomic beam 5 rises without pulled-in to the removing electrode, so that the separation efficiency of a atomic method laser isotope separation is improved.