The mechanism of synchronous oscillations found for reduction currents on two Pt electrodes in 0.7 M H2O2-0.3 M H2SO4 has been investigated. Synchronization occurs even when the two Pt working electrodes are far apart from each other if the distance between the working and reference electrodes is large enough. The synchronization also occurs even when one of the working electrodes is separated from the other electrodes with an electrically conductive carbon box. These results clearly indicate that the synchronization is not induced by mass transport but by electrical interaction. It is concluded that the current oscillation in one of the two oscillation systems causes an oscillation in the true electrode potential for the neighboring oscillation system through the oscillation of the ohmic drop in the solution, which leads to the synchronization.