PURPOSE: To provide a solid reference electrode which is provided with the performance required as reference electrode and can reduce dimension and provide an ion concentration sensor which is equipped with the solid reference electrode and can reduce the dimension of the whole device.

CONSTITUTION: A solid reference electrode D consists of a metal 11 and a solid electrolyte 10 and has the constitution in which the metal part 11 is desirably covered by a protecting film 12 and an inspected liquid 20 makes contact with the solid electrolyte 10, and an ion concentration sensor S is formed by connecting the solid reference electrode D with the feedback circuit F of an ion sensitive type electric field effect type transistor. Accordingly, a micro ion concentration sensor equipped with the performance required as ion concentration sensor be obtained.