An ion selective monoelectrode complex which is favorably employable to manufacture an ion activity measuring apparatus, has on a common non-electroconductive support sheet, plural ion selective monoelectrodes each of which is composed of an electrode composite consisting of, in order, a silver metal layer, a silver halide layer, an electrolytic material layer, and an ion selective membrane, and an electroconductive terminal which is electrically connected to the silver metal layer and which has an exposed surface, under the condition that the ion selective monoelectrodes are aligned, without electric contact with each other, along an imaginary line bridging the electrode composite and the electroconductive terminal.