PURPOSE: To measure automatically the ion concn. of an aq. soln. by controlling the transfer of vessels for the water to be inspected, the cleaning and moving of electrodes, etc. by a computer.

CONSTITUTION: A measuring device for ion concn. is constituted of a sample changer 2, an electrode 3, an electrode cleaning device 5, an electrode moving device 6, a computer control device 8, etc. The sample changer 3 consists of bisected rectangular box bodies, in which many vessel holders are arrayed and provided. Said chager is so constituted as to feed successively the vessels to be inspected provided in the holders to the measuring position when the holders are cyclically moved. The device 5 is provided with a cleaning ring 7 consisting of an annular body having water injecting holes 12 for spraying water to the electrodes 3 around the lower part thereof and core ejections holes 13 around the upper part thereof. The device 6 has the function to move the electrodes 3 between the vessels for the water to be inspected and the device 5. A series of operations to measure the ion concn. are carried out by the computer control device.