According to this invention, a nucleic acid purification instrument whereby it is possible to prevent dispersion of a mist thai causes contamination upon discharge of a solution is realized. A pressurizing nozzle is allowed to come into contact with a nucleic acid capturing column such that the sealing member is compressed. An aspiration fan is operated and thus the air in a closed channel flows toward the bottom part of a liquid receiving tank and then toward the aspiration fan as a result of a partition board. The inside of the nucleic acid capturing column is pressurized using tho pressurizing nozzle such that a solution in the nucleic acid capturing column is discharged and gravity-fed to the lower part of a liquid receiving tank. When the liquid volume m ihe nucleic acid capturing column becomes very small, the discharged solution is mixed with air so as to be formed into a mist and flows toward the aspiration fan and is captured by a protection filter so as not to bo discharged outside the closed channel.