The present invention provides an apparatus for separating and purifying nucleic acids, which comprises: a cylindrical syringe having a leading end part in which a first opening part is formed, a base end part in which a second opening part is formed and an accommodation part between said first opening part and second opening part, the accommodation part being able to hold liquid therein; and a solid phase-holding member connected to said leading end part, a flow hole being formed at the leading end side of the solid phase-holding member; wherein a solid phase comprised of an organic polymer having a hydroxyl group on the surface thereof is accommodated in said solid phase-holding member, the solid phase being able to adsorb and desorb nucleic acids in a sample solution; and wherein a pressure sensor capable of detecting the pressure in the accommodation part is connected.