Priming and fluid replacement for a blood purification device can be suitably carried out using a pump that has a liquid delivery flow rate and flow rate accuracy suited to priming. This blood purification device is provided with: a blood purifier (20) that is equipped with a blood purification membrane (30) a blood circuit (10) that sends blood in a blood collection portion (21) to a primary side of the blood purification membrane (30) using a blood pump (40) and returns the blood from the primary side to a blood return portion (23) a dialysis fluid supply circuit (91) that supplies a dialysis fluid to a secondary side of the blood purification membrane (30) a dialysis fluid discharge circuit (92) that discharges the dialysis fluid from the secondary side and a fluid replacement/priming circuit. Using the blood purification device, with the blood circuit (10) made to form a loop by connecting the blood collection portion (21) and the blood return portion (23), a fluid replacement pump (170) is used to make the dialysis fluid in the dialysis fluid supply circuit (91) pass through the blood purification membrane (30) and flow out to the primary side, and to discharge the dialysis fluid in the blood circuit (10) including the primary side into the dialysis fluid discharge circuit (92) without passing through the blood purification membrane (30).Linvention concerne un amorçage et un remplacement de fluide pour un dispositif de purification du sang qui peuvent être réalisés de manière appropriée à laide dune pompe qui présente un débit de distribution de liquide et une précision du débit adaptés à lamorçage. Ce dispositif de purification du sang comprend : un purificateur de sang (20) qui comporte une membrane de purification du sang (30) un circuit de sang (10) qui envoie du sang dans une partie de collecte de sang (21) à un côté primaire de la membrane de purification du sang (30) à laide dune pompe à sang (40) et renvoie le sang provenant du côté primaire à une part
