Abstract: A blood dialyzing apparatus includes a blood dialyzing filter for dialyzing blood by using a pressure difference between the blood and a dialysis solution, and a supplying means for supplying the blood and the dialysis solution to the blood dialyzing filter in order to alternately generate a state where a blood pressure is higher than a dialysis solution pressure and a state where the dialysis solution pressure is higher than the blood pressure. The blood dialyzing apparatus dialyzes a large volume of blood in a short period of time without increasing the size of the blood dialyzing filter and simply controls the volume of the dialyzed blood by adjusting the supply pressures of the blood and the dialysis solution.