According to this invention, an instrument and a method for nucleic acid isolation is realized, whereby it is possible to prevent, for example, adherence of a discharged solution upon dispersion of such solution to the vicinity of a nucleic acid isolation column outlet. A light source unit and a light-receiving unit that receives totally reflected light of the photosensor 41 for detecting the fluid level are placed on a site on the side surface of the nucleic acid isolation column 35, where the photosensor can detect the fluid level corresponding to a remaining liquid volume of approximately 10 ul. In addition, the light source unit of the photosensor 41 is positioned in a manner such that incident light is totally reflected from the interface between the nucleic acid isolation column 35 and air in the nucleic acid isolation column 35 and light is allowed to be incident in the solution when reaching the interface between the nucleic acid isolation column 35 and the solution in the nucleic acid isolation column 35. The light-receiving unit of the photosensor 41 is positioned in a manner such that it receives the totally reflected light and is fixed on the upper part of the nucleic-acid-adsorptive solid phase 24. The fluid level detection sensor is in communication with a syringe-driving motor 34 via a control unit 40 such that a syringe 31 is driven upward when the fluid level reaches a predetermined level, provided that a certain volume of the liquid remains in the nucleic acid isolation column 35. Accordingly, dispersion of the dispersed liquid is prevented.