PURPOSE: To minimize and stabilize potential difference between liquids and improve the accuracy of measurement, by providing a device wherein the internal liquid of a comparison electrode is hermetically sealed in an outer pipe except a liquid communication portion and a device for pressurizing and sucking the internal liquid in the outer pipe sealed up.

CONSTITUTION: Liquid is directly contacted and communicated in such a manner that a small cavity or a small tube portion 4 is installed to a nose of an outer pipe 2 housing internal liquid 3 and the internal liquid 3 is let flow out into liquid to be inspected 6 from the hole portion 5. An internal electrode 1 is hermetically sealed in the outer pipe 2 with the internal liquid 3, a branch pipe 7 is mounted to an upper portion of the outer pipe 2, and the branch pipe is connected to a pressurizing suction pump P3, a pressurizing suction device of the internal liquid, thus forming a comparison electrode portion. The solution concentration measuring device is constituted by a concentration indicating electrode ES, the comparison electrode ER, etc., and a liquid communication portion Rj (the small tube portion 4 and the hole portion 5) is inserted into a flow cell F.C with a detecting end of the concentration indicating electrode ES.