The size dependence of the frequency attenuation length (A) of extensive air showers has been studied at Akeno for electron sizes between lo5 and lo8.'. A decreases with increasing size up to lo6 and increases slowly above 10'. The value between lo7 and lo8 is 99 f 7 g cm-*. This indicates that the depth of the shower maximum above a few 10l6 eV is shallower than that obtained by optical methods and is consistent with that from the equiintensity cut method. The result supports the view that heavy enriched primary particles with a conservative interaction model or proton-dominated primaries with interactions of high multiplicity are required.