A phospholipid vesicle such as a virus is to be rapidly separated (concentrated, roughly purified) and good detection (diagnosis) results can be obtained with suppressing inhibition of virus-denature, PCR inhibition, latex-aggregation inhibition, and the like. Moreover, the above operations are to be automated. A phospholipid vesicle is separated using a water-soluble cationic magnetic fine particle by a composite formation through a covalent bond or physical adsorption of a substance having a cationic functional group, a substance having a hydroxyl group, and a substance having magnetism.