  The emission-line flux ratio of [O III]4363/[O III]5007 (R_OIII)is a useful
diagnostic for the ionization mechanism and physical properties of
emission-line regions in active galactic nuclei (AGNs). However, it is known
that simple photoionization models underpredict the [O III]4363 intensity,
being inconsistent with observations. In this paper, we report on several
pieces of evidence that a large fraction of the [O III]4363 emission arises
from the dense gas obscured by putative tori: (1) the visibility of high-R_OIII
regions is correlated to that of broad-line regions, (2) higher-R_OIII objects
show hotter mid-infrared colors, (3) higher-R_OIII objects show stronger
highly-ionized emission lines such as [Fe VII]6087 and [Fe X]6374, and (4)
higher-R_OIII objects have broader line width of [O III]4363 normalized by that
of [O III]5007. To estimate how such a dense component contributes to the total
emission-line flux, dual-component photoionization model calculations are
performed. It is shown that the observed values of R_OIII of type 1 AGNs may be
explained by introducing a 5% - 20% contribution from the dense component while
those of type 2 AGNs may be explained by introducing a 0% - 2% contribution. We
also discuss the [O III]4363 emitting regions in LINERs in the framework of our
dual-component model.
