PURPOSE: To simplify extraction of nucleic acid and provide high yield in the field, etc., of genetic engineering by adding a protein modifying agent to a nucleic acid-containing sample, then adding an alcohol thereto and recovering formed precipitates.

CONSTITUTION: A protein modifying agent (preferably 2.5-5.5M guanidine thiocyanate and ≥6M urea) is converted into the form of a solution, etc., and added to a sample such as tissue, blood or sputum (if the sample has cell wall, etc., or is in the form of a lump, treatment such as homogenization, as necessary, is carried out) and an adequate amount of an alcohol (preferably ethanol, etc.) is then added to centrifuge formed precipitates, etc. Thereby, the objective nucleic acid is extracted or removed.