  We investigate gas metallicity of narrow-line regions in narrow-line Seyfert
1 galaxies (NLS1s) and broad-line ones (BLS1s) in order to examine whether or
not there is a difference in the gas metallicity between the two populations of
Seyfert 1 galaxies. We apply two methods to study this issue. One is to use the
emission-line flux ratio of [N II]6583/H_alpha in combination with some other
optical emission-line flux ratios. This method, which has been often applied to
Seyfert 2 galaxies, suggests that the gas metallicity of narrow-line regions is
indistinguishable or possibly higher in BLS1s than in NLS1s. On the contrary,
the other method in which only forbidden emission-line fluxes are used results
in that NLS1s tend to possess metal-richer gas in the narrow-line regions than
BLS1s. We point out that this inconsistency may be owing to the contamination
of the broad component of permitted lines into the narrow component of ones in
the first method. Since the results derived by using only forbidden
emission-line fluxes do not suffer from any uncertainty of the fitting function
for the broad component of Balmer lines, the results from this method are more
reliable than those derived by using permitted lines. We thus conclude that the
gas metallicity of narrow-line regions tends to be higher in NLS1s than in
BLS1s.
