The influences of electrode-surface modifications and structural changes on an electrochemical oscillation of a negative differential resistance (NDR) type, observed for H2O2 reduction on Pt electrodes in acidic solutions, and previously called oscillation A, were investigated. For Pt electrodes coated with a submonolayer amount of Ru atoms, the oscillation period became shorter than that for naked Pt, whereas for Pt coated with a submonolayer amount of iodine atoms, the period became longer. For naked Pt immersed in solutions containing a small amount of Cu2+, Ru3+, and AuCl4-, the oscillation period became shorter with time, whereas it became longer in solutions containing Ag+. For Pt-layer electrodes with island structure, formed by vacuum deposition on single-crystal p-Si wafers, the oscillation period became longer with the increasing size of the islands. Such modulations of the oscillation period were all explained by considering three types of electrode surfaces, a surface (such as naked Pt) on which the H2O2 reduction occurs oscillatorily, a surface (such as a Ru-covered part) on which it occurs steadily, and a surface (such as an iodine-covered pan) on which no H2O2 reduction occurs. Mathematical simulation showed that the oscillation period was determined by the ratios of the areas of these surfaces, which were mixed at the electrode surface on atomic or nanometer scales.