The objective of the present invention is to provide a dialysis device and a fluid replacement control method capable of carrying out appropriate fluid replacement.A dialysis device 100 is provided with a blood circuit 110, a blood purifying means 120, a dialysate circuit 130, a circulating blood quantity measuring means 140, a replenishing liquid injecting means for injecting into the blood circuit replenishing liquid for restoring the circulating blood quantity, and a control unit 150 for controlling the replenishing liquid injecting means in such a way that a predetermined quantity of the replenishing liquid is injected intermittently into the blood circuit at predetermined intervals, wherein the control unit adjusts the next replenishing liquid injection quantity and/or injection interval in such a way that a rate of change in the circulating blood quantity resulting from the next replenishing liquid injection lies in a predetermined range, on the basis of the rate of change in the circulating blood quantity resulting from the most recent injection of replenishing liquid, measured using the measuring means, and controls a rate of water removal by the blood purifying means in such a way that water content corresponding to the entire quantity of replenishing liquid injected into the blood circuit is recovered during the period from the start to the end of the dialysis.L'objectif de la présente invention est de fournir un dispositif de dialyse et un procédé de commande de remplacement de fluide capables de réaliser un remplacement de fluide approprié. Un dispositif de dialyse 100 est pourvu d'un circuit sanguin 110, d'un moyen de purification de sang 120, d'un circuit de dialysat 130, d'un moyen de mesure de quantité de sang circulant 140, d'un moyen d'injection de liquide de réapprovisionnement permettant d'injecter dans le circuit sanguin un liquide de réapprovisionnement pour restaurer la quantité de sang circulant, et d'une unité de commande 150 pour commande
