PURPOSE: To separate substances having magnetic moment when ionized from a substance having no magnetic moment by evaporating and ionizing a substance to be purified in a vacuum vessel and by carrying out attraction and collection while changing the concn. of impurities in the ionized substance by applying a magnetic field.

CONSTITUTION: A cylindrical vacuum vessel 1 made of stainless steel is kept at a suitable vacuum degree with a vacuum pump while introducing Ar. A substance to be purified such as Al 4 in an evaporator 3 is evaporated by heating with a heater 5, and the vapor is ionized with a pair of high frequency electrodes as ionizers 6, 6'. A magnetic field is applied to the ions with an electromagnet 7 as a magnetic field generator, and the concn. of impurities such as U and Th ions is increased in the vicinity of the field. Al with higher U and Th content and Al with lower U and Th content are collected with the 1st substance collectors 8, 8' which are a pair of electrostatic electrodes and the 2nd substance collectors 9, 9', respectifely. By repeating said separation, U and Th ions having magnetic moment are separated from Al ions having no magnetic moment.