To provide a blood purification device capable of accurately acquiring colloid osmotic pressure or a correlation value of colloid osmotic pressure using a purification membrane of a blood purifier and accurately estimating a patient's nutritional state, and also provide a patient's nutritional state estimation method by the blood purification device.SOLUTION: There is provided a blood purification device capable of acquiring colloid osmotic pressure of the blood flowing in a blood flow path or a correlation value of the colloid osmotic pressure on the basis of a transmembrane pressure difference (TMPa) generated when a priming liquid, which is a liquid in which colloid osmotic pressure is not generated, is put in a blood flow path in a state that filtration by a water removal pump 8 is not carried out, and a transmembrane pressure difference (TMPb) generated when the patient blood is put in the blood flow path in a state that filtration by the water removal pump 8 is not carried out. There is also provided a patient's nutritional state estimation method by the blood purification device.SELECTED DRAWING: Figure 1【課題】血液浄化器の浄化膜を利用して膠質浸透圧又は膠質浸透圧の相関値を精度よく求めることができ、患者の栄養状態を正確に推定することができる血液浄化装置及び血液浄化装置による患者の栄養状態の推定方法を提供する。【解決手段】除水ポンプ８による濾過が行われていない状態で、膠質浸透圧が発生しない液体であるプライミング液を血液流路に充填させた場合に生じる膜間圧力差（ＴＭＰａ）と、除水ポンプ８による濾過が行われていない状態で、患者の血液を血液流路に充填させた場合に生じる膜間圧力差（ＴＭＰｂ）とに基づいて、血液流路を流れる血液の膠質浸透圧又は当該膠質浸透圧の相関値を取得可能な血液浄化装置及び血液浄化装置による患者の栄養状態の推定方法である。【選択図】図１
