PURPOSE: To efficiently remove a pyrogenic material (pyrogen) by treating a liquid containing pyrogen with a cation exchanger and then by further treating the treated liquid with a pyrogen adsorption substance.

CONSTITUTION: A pyrogen containing liquid 2 is treated with a cation exchanger 4 and then the treated liquid is further treated with a pyrogen adsorbing substance 5 (e.g., L-histidine holding agarose). Pyrogen is thus efficiently removed from the liquid containing it. This de-pyrogened water is usable for medical use such as dialysis water of artificial dialysis for a patient with renal insufficiency, supply water for filtration-type artificial kidney, preparation of dilute solution from highly concentrated instillation medicine at bed side, etc., or for washing medical tools.