A hemodialysis, apparatus comprising: a dialysis device configured to dialyze and ultrafiltrate blood of a patient according to an ultrafiltration volume based on an estimated dry weight of the patient, while performing hemodialysis treatment on the blood circulating extracorporeally; a detecting device configured to obtain time series data indicating the trend of circulating blood volume rate with the passage of time by measuring a parameter related to concentration of the blood circulating extracorporeally at a plurality of points in time series in a process of the hemodialysis treatment by the dialysis device; a memory device configured to cumulatively store a plurality of subsequent time series data of hemodialysis treatments; a calculation device; characterized in that the apparatus further comprises an evaluation device configured to evaluate appropriateness of the hemodialysis treatment by evaluating whether the estimated dry weight, which is estimated before the hemodialysis treatment based on experiences of a medical staff approximates to a dry weight of the patient, and in that the memory device is configured to store, among the subsequent time series data obtained by the detection device, the plurality of subsequent time series data from hemodialysis treatments which have been evaluated to be appropriate by the evaluation device, and the time series data stored in the memory device is standardized by performing a predetermined operation to obtain universal time series data unrelated to specific conditions of a particular patient such as a body weight and an ultrafiltration volume of the patient; the calculation device is configured to calculate an optimal change in the time series data expected in an appropriate process of the hemodialysis treatment based on the plurality of subsequent time series data stored in the memory device and to calculate an optimal range of change having a predetermined range between a lower limit and an upper limit at each measuring point of the parameter related to concentration of the blood circulating extracorporeally. a dialysis device configured to dialyze and ultrafiltrate blood of a patient according to an ultrafiltration volume based on an estimated dry weight of the patient, while performing hemodialysis treatment on the blood circulating extracorporeally; a detecting device configured to obtain time series data indicating the trend of circulating blood volume rate with the passage of time by measuring a parameter related to concentration of the blood circulating extracorporeally at a plurality of points in time series in a process of the hemodialysis treatment by the dialysis device; a memory device configured to cumulatively store a plurality of subsequent time series data of hemodialysis treatments; a calculation device; characterized in that the apparatus further comprises an evaluation device configured to evaluate appropriateness of the hemodialysis treatment by evaluating whether the estimated dry weight, which is estimated before the hemodialysis treatment based on experiences of a medical staff approximates to a dry weight of the patient, and in that the memory device is configured to store, among the subsequent time series data obtained by the detection device, the plurality of subsequent time series data from hemodialysis treatments which have been evaluated to be appropriate by the evaluation device, and the time series data stored in the memory device is standardized by performing a predetermined operation to obtain universal time series data unrelated to specific conditions of a particular patient such as a body weight and an ultrafiltration volume of the patient; the calculation device is configured to calculate an optimal change in the time series data expected in an appropriate process of the hemodialysis treatment based on the plurality of subsequent time series data stored in the memory device and to calculate an optimal range of change having a predetermined range between a lower limit and an upper limit at each measuring point of the parameter related to concentration of the blood circulating extracorporeally.