The present invention provides a blood purification device, comprising: a blood circuit including an artery-side blood circuit attached with an artery-side puncture needle capable of piercing access vessels of a patient and a vein-side blood circuit attached with a vein-side puncture needle capable of piercing the access vessels, the blood circuit being capable of extracorporeally circulating bloods of the patient； a blood purifier connected between the artery-side blood circuit and the vein-side blood circuit, for purifying bloods flowing through the blood circuit； a blood pump provided to the artery-side blood circuit； a recirculated blood detection unit capable of detecting recirculated bloods that have been returned to the patient from the vein-side blood circuit and guided to the artery-side blood circuit to flow therethrough again when the blood pump is driven to extracorporeally circulate the bloods of the patient through the blood circuit； and a recirculation rate calculation unit capable of calculating a recirculation rate which is a proportion of the recirculated bloods in bloods flowing through the artery-side blood circuit, wherein the blood purification device is characterized by comprising a control unit capable of executing: a therapy mode in which blood purification therapy is performed by the blood purifier while the blood pump is driven in a forward connection state in which a puncture needle at a tip of the artery-side blood circuit is pierced on an upstream side of the access vessels and a puncture needle at a tip of the vein-side blood circuit is pierced on a downstream side of the access vessels such that the bloods of the patient are extracorporeally circulated through the blood circuit； and a measurement mode in which recirculated bloods are detected by the recirculated blood detection unit and a recirculation rate is calculated by the recirculation rate calculation unit while the blood pump is driven in a reverse connection state in which th
