A blood purification device suitable for use with a blood circuit and with a blood purifier attached to the blood circuit , said blood circuit including an arterial side line (LA) and a venous side line (LV), wherein the arterial side line (LA) and the venous side line (LV) are connected to both ends of the blood purifier , the blood purification device comprising: a blood pump (PB) to be provided midway in the arterial side line (LA); a control part ; a dialysis fluid tank that stores dialysis fluid; a lead-in line (LI) to connect the dialysis fluid tank and the blood purifier ; a lead-out line (LO) to connect the dialysis fluid tank and the blood purifier ; a lead-in pump (PI) provided midway in the lead-in line (LI); a lead-out pump (PO) provided midway in the lead-out line (LO); and a supplying part and a discharging part , or alternatively, one container , wherein in a state in which the supplying part or the one container that supplies priming fluid and the venous side line (LV) are connected via a venous side connector (CV) provided at a distal end of the venous side line (LV), and the discharging part or the one container from which the priming fluid after use is discharged and the arterial side line (LA) are connected via an arterial side connector (CA) provided at a distal end of the arterial side line (LA), the control part is configured, when receiving instruction for priming execution, to drive the blood pump (PB) and to execute first priming processing for priming the blood circuit and the blood purifier , and the control part is configured, after the first priming processing, to drive the lead-in pump (PI) and the lead-out pump (PO) and to execute second priming processing for feeding the priming fluid to the lead-in line (LI) and the lead-out line (LO). a blood pump (PB) to be provided midway in the arterial side line (LA); a control part ; a dialysis fluid tank that stores dialysis fluid; a lead-in line (LI) to connect the dialysis fluid tank and the blood purifier ; a lead-out line (LO) to connect the dialysis fluid tank and the blood purifier ; a lead-in pump (PI) provided midway in the lead-in line (LI); a lead-out pump (PO) provided midway in the lead-out line (LO); and a supplying part and a discharging part , or alternatively, one container , wherein in a state in which the supplying part or the one container that supplies priming fluid and the venous side line (LV) are connected via a venous side connector (CV) provided at a distal end of the venous side line (LV), and the discharging part or the one container from which the priming fluid after use is discharged and the arterial side line (LA) are connected via an arterial side connector (CA) provided at a distal end of the arterial side line (LA), the control part is configured, when receiving instruction for priming execution, to drive the blood pump (PB) and to execute first priming processing for priming the blood circuit and the blood purifier , and the control part is configured, after the first priming processing, to drive the lead-in pump (PI) and the lead-out pump (PO) and to execute second priming processing for feeding the priming fluid to the lead-in line (LI) and the lead-out line (LO). <EOS>