An electrochemical reactor includes positive and negative electrodes. A conductive and/or dielectric liquid is provided between the positive and negative electrodes. A first isolation member provided on the positive electrode isolates the positive electrode from the liquid, and a second isolation member provided on the negative electrode isolates the negative electrode from the liquid. The first and second isolation member each includes a liquid-repellent porous membrane. The reactor further includes a pressure-applying member which pressurizes the liquid to fill the pores of the first and second liquid-repellent porous membranes with the liquid, thereby causing an electrochemical reaction involving the positive and negative electrodes.