Chemical oscillation induced by ionic surfactant molecules at a water (W)/nitrobenzene (NB) interface is investigated by simultaneous monitoring of electrochemical potential and interfacial tension. The presence of hydrophilic ions in the organic (NB) phase is found to drastically accelerate the relaxation process of electrical potential, indicating that ion exchange critically affects the desorption of ionic surfactant molecules from the interface and the deformation of an electrical double layer at the interface. In addition, two-step relaxation of the electrical potential is found, that provides information on the origin of the electrical potential generated in chemical oscillations. The mechanism for the nonlinear oscillatory behavior of the ionic surfactant molecules at the W/NB interface is considered in terms of the remarkable difference in diffusion speed in the aqueous bulk phase and across the W/NB interface due to the contribution of the water molecules that hydrate the surfactant molecules.