PURPOSE: To sense the concentration of dialysis liquid highly accurately in a broad temperature range and to make the constitution of the concentration meter simple and compact by computing conductivity data by a microcomputer.

CONSTITUTION: The temperature and the conductivity of blood dialysis liquid and the like are sensed by a temperature sensing element 2 and a conductivity sensing element 3 in a concentration measuring cell 1, a temperature sensing circuit 4, and a conductivity sensing circuit 5. The A/D conversion of the sensed values is performed, and the results are imputted to a CPU10 in the microcomputer, where the computation based on concentration function formula with the electric conductivity and the temperature stored in ROM11 as the functions is performed. The resulting concentration values are displayed on a display 15 via RAM12. In this method wherein temperature compensating thermistor and the like are not used, the concentration of the dialysis liquid is detected highly accurately in the broad temperature range, and the constitution of the concentration meter is made to be simple and compact.