To provide a nucleic acid-extracting apparatus capable of automatically and efficiently extracting a nucleic acid in a sample liquid in a short time and preventing occurrence of contamination caused by pressurizing air acting on an extraction cartridge to raise reliability.

The nucleic acid-extracting apparatus carries out extraction action of pressurizing the sample liquid by using an extraction cartridge equipped with a filter member to absorb a nucleic acid and removing impurities with a washing liquid and recovering the nucleic acid by a recovering liquid. The apparatus is equipped with a carrying mechanism 3, a pressurizing air feed mechanism 4 and a dispensing mechanism 5. The pressurizing air feed mechanism 4 is equipped with one air pump 43, an opening and closing valve 45 for opening and closing passage to the extraction cartridge 11, a pressure sensor 46 for detecting cartridge inner pressure and a relief valve 44 for opening the upstream pressure of the opening and closing valve 45 into the air, and opening operation of the opening and closing valve 45 is carried out at a point of time finishing pressuring after liquid discharge is completed and pressurizing air remaining in the extraction cartridge 11 is opened to the air to prevent scattering and jetting of liquid.