PROBLEM TO BE SOLVED: To provide a method for detecting a needle withdrawal of an extracorporeal blood circulation type device, which can quickly identify whether the puncture needle is a puncture needle of a blood circuit on the blood removal side or a puncture needle of blood on the blood return side. Is the subject. SOLUTION: A blood processor is connected between a blood removal side blood circuit having a blood removal side puncture needle at the tip and a blood return side blood circuit having a blood return side puncture needle at the tip, and one electrode is removed. It is installed in either the blood side blood circuit, the blood return side blood circuit, or the part that electrically conducts to the blood flowing inside the blood processor, and the other electrodes are installed in contact with the surface of the patient's body. It is formed by a blood removal side electric circuit that leads from one electrode to another electrode via an electrical path formed by blood passing through the blood removal side puncture needle, and blood passing through the blood return side puncture needle from one electrode. A needle removal detection method in which a blood-returning electric circuit that leads to another electrode via an electric path forms a parallel relationship in an electric circuit, measures the impedance between both electrodes, and detects needle removal. [Selection diagram] Fig. 1【課題】穿刺針の抜針がすみやかにかつ、脱血側血液回路の穿刺針か返血側血液の穿刺針かの特定がすみやかにできる血液体外循環型装置の抜針検出方法を提供することを課題とする。【解決手段】脱血側穿刺針を先端に有する脱血側血液回路と、返血側穿刺針を先端に有する返血側血液回路との間に血液処理器が接続され、一の電極が脱血側血液回路、返血側血液回路、又は、血液処理器の内部を流れる血液に電気的に導通する部分のいずれかに設置され、他の電極が患者の身体表面部に接して設置され、一の電極から脱血側穿刺針を通る血液にて形成される電気経路を経て他の電極に通じる脱血側電気回路と、一の電極から返血側穿刺針を通る血液にて形成される電気経路を経て他の電極に通じる返血側電気回路とが、電気回路的に並列の関係を形成し両電極間のインピーダンスを測定し抜針を検出する抜針検出方法。【選択図】 図１
