A high-purity fragment is obtained by a simple mechanism and method for separating and purifying a nucleic acid, particularly fragment DNA, extremely efficiently and with a high reproducibility, wherein elution with a high-concentration salt is not performed and necessity of elution and purification is eliminated.This mechanism is a mechanism for purifying a nucleic acid, particularly fragment DNA using a monolith structure formed with glass or silica, specifically, an integral porous body having an open structure with pores that communicate the upper end with the lower end, wherein through-pores corresponding to nucleic acid sizes of 35 bp (mer) to 100 Kbp (mer) are provided.
