A hemodialysis apparatus 1 is provided with a dialyzer 2 for performing hemodialysis, a blood circuit 3 connected to the dialyzer, a dialysis solution circuit 4 connected to the dialyzer, a replacement fluid port 31 provided in the dialysis solution circuit and capable of being opened and closed by a lid member, and a replacement fluid passage 6 having its one end connected to the blood circuit and the other end connected to the replacement fluid port. After a dialysis fluid substitution step of filling the dialysis solution circuit with a dialysis solution, the lid member is detached from the replacement fluid port to change the replacement fluid port from a closed state to an open state. To connect the replacement fluid passage to the replacement fluid port in the open state, a negative pressure forming step to make the pressure in the dialysis solution circuit negative is performed after the dialysis fluid substitution step. The replacement fluid port is thereafter changed from the closed state to the open state. Overflowing of the dialysis solution from the replacement fluid port is prevented to enable performing operations in a sanitary manner.
