To separate genes and nucleic acids in biological samples from microorganisms and cells, as the impurities are reduced.

When the genes and the nucleic acids in biological samples are isolated from impurities, the sample is introduced into the hollow parts of capillary tubes to trap the genes and nucleic acids on the wall 2 of the capillary in the first step, unneeded concomitant components 3 are washed and removed off in the second step and the trapped genes and nucleic acids are eluted from the capillary in the third step.