Absolute values of changes in surface energy of gold electrode in perchlorate solutions with and without iodide ions were measured by a laser-beam deflection method. The potential of the electrocapillary, maximum or potential of zero charge (pzc) obtained by the laser-beam deflection method was in good agreement with that obtained previously by a piezoelectric technique. The derivative of surface energy with electrode potential, -(partial derivative gamma(s)/partial derivative E), was quits different from the surface charge density, q(m), obtained with integration of current density in the cyclic voltammogram, indicating that the simple Lippmann equation, that is, -(partial derivative gamma(s)/partial derivative E) = q(m), did not hold. Particularly. -(partial derivative gamma(s)/partial derivative E) took a maximum near the potential at which the charge transfer of adsorbed iodide ions occurred to form the iodine adlayer despite the fact that q(m) increased monotonically with increasing potential. The above results obtained by the laser-beam deflection method were also consistent with those obtained previously by the piezoelectric technique. The discrepancy between -(partial derivative gamma(s)/partial derivative E) and q(m) was ascribed to the changes in surface elastic strain accompanied by the structural changes of the adlayer.