PURPOSE: To lower the costs by arranging solidifying enzyme film electrodes at sections of measuring urea nitrogen, creatinine and glycol separately formed while connecting the measuring sections with a line pipe.

CONSTITUTION: Pumps P1, P2 and P3 are operated to clean a measuring line L1 and a compensating line L2 with a buffer and then, 6-way valves V1 and V2 are turned by a specified angle to retain a constant amount of sample injected from A1'. The constant amount of the sample is fed to mixing coils M1 and M2 by turning the 6-way valves V1 and V2 by a specified angle again. Urea nitrogen of the samle from the mixing coils M1 and M2 is measured with an electrode 1 and NH+4 thereof with an electrode 4. The measuring signal is transmitted to a computer 7 to calculate urea nitrogen correctly. A creatinine measuring electrode 2 and a creatinine measuring electrode 5 are combined to determine creatine correctly. After the completion of the measurement, glycol is measured with a measuring electrode 3.