PURPOSE: To enable simultaneous analysis of Na+, K+, Ca++, Cl- in blood by using an internal standard liquid contg. a weak acidic salt, a standard liquid for calibrating the sensitivity of ion electrodes and a standard liquid for correcting activity of Ca++ contg. no weak acidic salt.

CONSTITUTION: The inlet side of a flow cell 7 provided with ion electrodes 1W4 (Na+, K+, Ca++, Cl-) and a comparing electrode 5 as well as a measuring chamber 6 is communicated via a suction nozzle 8 to an internal standard liquid 11 or a sample 12 and the outlet side via conduits 9, 10 and a liquid feed pump 13 with the outside of he system. The electrodes 1W4 and the electrode 5 disposed to contact with the test liquid flowing through the inside of the chamber 6 in the sensitive part are conducted by lead wires 14W18 to the input side of amplifiers 23W26 and the output side of amplifiers 23W26 are conducted by lead wires 19W26 to a recorder 27. If the operation of the pump 13 is stopped while the nozzle 8 is inserted into the liquid 11 or sample liquid 12 by such device, the internal standard liquid or the sample liquid is temporarily stagnated in the chamber 6. The response potentials of the electrodes 1W4 in this stage are recorded in a recorder 27.