To perform all the isotope separations including uranium enrichment by one-step operation and to provide a technique of constituting an ultrahigh purity ion source or plasm source.

Only an object isotope element to be separated is separated by utilizing a parametric resonance phenomenon. The principle of operation is as follows. First, an isotope element is made plasma by a plasma source 01, and is led to a high frequency quadrupole 05 present in the central part. High frequency waves of frequency about two times the ion cyclotron frequency of the object isotope element are applied there, and only the object isotope is selectively accelerated and overcomes the voltage of a blocking electrode 06 and is recovered by a recovery electrode 7. Since other elements are not accelerated, they cannot overcome the blocking voltage.