  In order to examine the prediction that the broad-line radio galaxies (BLRGs)
with double-peaked Balmer lines harbor an accretion disk characterized by an
advection-dominated accretion flow (ADAF) in their nuclei, we investigate
narrow emission-line flux ratios of the narrow-line regions which are
photoionized by the nuclear continuum radiation. We compile data from the
literature and confirm the pioneering work of Eracleous & Halpern that the
BLRGs with the double-peaked Balmer emission exhibit larger flux ratios of both
[O I]6300/[O III]5007 and [O II]3727/[O III]5007 than the BLRGs without the
double-peaked Balmer emission. To examine whether or not these properties are
attributed to the difference in the spectral energy distribution (SED) of the
ionizing radiation between the BLRGs with and without the double-peaked Balmer
emission, we perform photoionization model calculations using two types of
input continuum radiation; one has the strong big blue bump which is expected
for standard optically-thick accretion disks and another does not exhibit a
strong big blue bump as expected for optically-thin ADAFs. We find that the
data of the BLRGs with the double-peaked Balmer lines are consistent with the
models adopting the SED without a strong big blue bump while the data of the
BLRGs without the double-peaked emission lines are well described by the models
adopting the SED with a strong big blue bump. On the other hand, the observed
differences in the NLR emission is hard to be explain by the difference in the
contribution of shocks. These results support the idea that the double-peaked
Balmer lines arise at an outer region of an accretion disk which is illuminated
by an inner, geometrically-thick ADAF.
