PROBLEM TO BE SOLVED: To efficiently perform priming of a blood purifier in a simple method.SOLUTION: The blood purifier is adapted to supply a dialysate to a vein side blood passage 30 by a replenisher pump 41 and to reversely rotate a blood pump 21 so that the fluid feed flow rate of the blood pump 21 is smaller than the feed flow rate of the dialysate by the replenisher pump 41, thereby ejecting air initially filled in a dialyzer 10, an artery side blood passage 20 and the vein side blood passage 30, from an air ejection passage 38 to perform priming of the dialyzer 10, the artery side blood passage 20 and the vein side blood passage 30.
