An object of the present application is to improve the measurement accuracy of a concentration measuring device of a therapeutic fluid preparation device, without increasing the burden to healthcare workers during a preparation stage for treatment, such as continuous treatment, and without the need to add further functions to a sensor.The invention relates to a therapeutic fluid preparation device for preparing therapeutic fluid having a predetermined concentration by mixing a plurality of stock solutions, the device comprising:a mixing circuit in which the plurality of stock solutions are mixed；a concentration measuring device having an electric conductivity sensor that measures an electric conductivity of a solution mixture in the mixing circuit and a temperature sensor that measures a temperature of the solution mixture, the concentration measuring device measuring a concentration of the solution mixture in accordance with the measured electric conductivity by the electric conductivity sensor and the measured temperature by the temperature sensor；electrolyte supply means that supplies an electrolyte having a known concentration through the mixing circuit with a temperature of the electrolyte being varied；calibration curve generating means that directs the electrolyte supply means to supply the electrolyte having the known concentration through the mixing circuit with varying temperatures, that measures an electric conductivity of the supplied electrolyte using the electric conductivity sensor, that also measures a temperature of the supplied electrolyte using the temperature sensor, and that thereby generates a calibration curve between electric conductivity and temperature； andconcentration calculating means that measures the electric conductivity and the temperature of the solution mixture in the mixing circuit using the electric conductivity sensor and the temperature sensor, that determines, on the calibration curve, the electric conductiv
