Dialysis device and control method

The invention provides a dialysis device and a method for controlling water removal speed, which can reduce the burden of a patient according to the circulation dynamic state of the blood after the replenishing liquid is injected. This dialysis device (100) is provided with: a blood circuit (110); a blood purification unit 120; a dialysate circuit 130; a circulating blood volume measurement means (140); a replenisher injection unit for injecting replenisher into the blood circuit 110; and a control unit (150) that controls the replenisher injection unit so as to intermittently inject a predetermined amount of replenisher into the blood circuit (110) at a predetermined interval, and that controls the replenisher injection unit (150) so as to inject the replenisher into the blood circuit (110) when the water in the blood is removed by the blood purification unit (120). When the decreasing speed of the rate of change after the end of the injection of the replenishing liquid measured by the circulating blood amou