Blood purifying apparatus

A blood purifying apparatus having excellent purification performance (elimination of low molecular proteins, etc.) and being contaminated with little endotoxins flowing from the dialyzate side. Attention was paid to the solute permeability coefficient alpha and water permeability performance Lp of blood purifying apparatus and the relation between alpha and Lp has been examined. As a result, a blood purifying apparatus having excellent purification performance and substantially being free from invasion of endotoxins was obtained by regulating the value alpha /Lp to 6x10 or above, or regulating alpha within a range of 8x10 to 1.5x10, and the value alpha x Lp to 2.4x10 or less. Also, a blood purifying apparatus having excellent purification performance and substantially being free from invasion of endotoxins was obtained by regulating the invasion ratio which is obtained by the polymer invasion test to 10% or less. The blood purifying apparatus has an excellent blood purifying performance expressed typically by the elimination ratio of low-molecular weight proteins and is substantially free from invasion of endotoxins from the dialyzate side, which makes it useful in, for example, treating patients with renal dysfunction.