The invention is to provide a kind of blood dialyzing device. It can accurately detect the disentanglement of the needle from patient in the blood dialysis by means of the voltage provided by the blood flowing through the blood circuit and monitoring the voltage difference of the prescribed part, while preventing from the increase of manufacturing cost due to the disposable blood circuit product. The blood dialysis apparatus comprises:artery side blood circuit 1a and vein side blood circuit 1bblood pump 3dialyzer 2dialysis apparatus body 6 with dialytic liquid introducing tube L1 and dialytic liquid ejecting tube L2voltage supplying mechanism 5detecting mechanism for detecting voltage 12monitoring mechanism 15 for monitoring the disentanglement of the needle from patent according to the voltage of detecting mechanismwherein an electrode 5a of voltage supplying mechanism is disposed between the needle (a) of the artery side and blood pump in the artery side blood circuit 1a and the other electrode is disposed on the dialytic liquid ejecting tube L2.本發明提供一種血液透析裝置,藉由對流過血液流路的血液賦予電壓並監視規定部位的電位差,可以正確地檢測血液透析治療中的從患者身上的穿刺針脫落,同時可以抑制作為拋棄式用品的血液流路的製造成本的增加。在血液透析裝置中包括:動脈側血液流路1a及靜脈側血液流路1b;血液泵3;透析器2;具有透析液導入導管L1及透析液排出導管L2的,透析裝置本體6;電壓賦予機構5;檢測電位的檢測機構12;以及根據該檢測機構12的電位來監視穿刺針從患者身上脫落的監視機構15,電壓賦予機構5的一方電極5a配置在動脈側血液流路1a中的動脈側穿刺針a和血液泵3之間,且另一方電極5b配置在透析液排出導管L2上。1...血液流路1a...動脈側血液流路1b...靜脈側血液流路2...透析器2a...血液導入埠2b...血液導出埠2c...透析液導入埠2d...透析液導入管3...血液泵4...滴漏室5...電極賦予機構5a...一方之電極5b...另一方之電極6...透析裝置本體12...檢測機構(接點)A...動脈側穿刺針B...靜脈側穿刺針L1...透析液導入導管L2...透析液排出導管H1、H2...佈線