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. In one aspect of the present invention, a therapeutic fluid preparation device (60) includes: a mixing circuit (70) for mixing a plurality of stock solutions therein； a concentration measuring device (71) that measures the concentration of a solution mixture in accordance with the electric conductivity and temperature measured by an electric conductivity sensor (120) and a temperature sensor (121), respectively； an electrolyte supply means (72) that supplies an electrolyte having a known concentration through the mixing circuit (70)； and a calibration means (73) that directs the electrolyte supply means (72) to supply the electrolyte having the known concentration through the mixing circuit (70), that measures the electric conductivity of the supplied electrolyte using the electric conductivity sensor (120), and that calibrates the temperature sensor (121) based on the difference between the measured electric conductivity and a known electric conductivity of the electrolyte by referring to a correlation between temperature and electric conductivity.
