A dialysis fluid preparation apparatus for ameliorating metabolic acidosis, comprising: an agent S container that accommodates an agent S containing sodium chloride and has an outlet, an agent B container that accommodates an agent B containing sodium bicarbonate and has an outlet, an agent A container that accommodates an agent A containing a combination of electrolyte components other than sodium chloride and sodium bicarbonate and has an outlet, a mixing part in which the agent S discharged in use from the agent S container, the agent B discharged in use from the agent B container, and the agent A discharged in use from the agent A container are mixed in use to give a dialysis fluid, an input part that, in use, receives an input of dialysis fluid data containing bicarbonate concentration information that specifies a bicarbonate ion concentration in the dialysis fluid, wherein the bicarbonate ion concentration is set according to the disease state of a patient and set to change over time during dialysis according to an adjustment program, and a control part that, in use, controls at least an amount of the agent B supplied to the mixing part based on the dialysis fluid data so as to change the bicarbonate ion concentration in the dialysis fluid over time during dialysis according to the adjustment program, the control part configured to control in use the amount of the agent B supplied to the mixing part based on the bicarbonate concentration information, and controlling at least one of the amount of the agent S and the amount of the agent A supplied to the mixing part such that the sodium ion concentration in the dialysis fluid is at a constant level. an agent S container that accommodates an agent S containing sodium chloride and has an outlet, an agent B container that accommodates an agent B containing sodium bicarbonate and has an outlet, an agent A container that accommodates an agent A containing a combination of electrolyte components other than sodium chloride and sodium bicarbonate and has an outlet, a mixing part in which the agent S discharged in use from the agent S container, the agent B discharged in use from the agent B container, and the agent A discharged in use from the agent A container are mixed in use to give a dialysis fluid, an input part that, in use, receives an input of dialysis fluid data containing bicarbonate concentration information that specifies a bicarbonate ion concentration in the dialysis fluid, wherein the bicarbonate ion concentration is set according to the disease state of a patient and set to change over time during dialysis according to an adjustment program, and a control part that, in use, controls at least an amount of the agent B supplied to the mixing part based on the dialysis fluid data so as to change the bicarbonate ion concentration in the dialysis fluid over time during dialysis according to the adjustment program, the control part configured to control in use the amount of the agent B supplied to the mixing part based on the bicarbonate concentration information, and controlling at least one of the amount of the agent S and the amount of the agent A supplied to the mixing part such that the sodium ion concentration in the dialysis fluid is at a constant level.