  As a newly discovered class of radio-loud active galactic nuclei (AGNs), the
\gamma-ray detected narrow-line Seyfert 1 galaxies (NLS1s) launch powerful jets
which are generally found only in blazars and radio galaxies. However, their
black hole (BH) masses as estimated from the broad emission lines are one order
of magnitude or more lower than those in blazars. This brings new challenges
for explaining the radio loudness triggering in AGNs. It is still under debate
whether their BH masses from the commonly used virial method are
underestimated. Here we present an estimate of the BH mass for the \gamma-ray
detected NLS1 1H 0323+342, an archetype of this class, from the X-ray
variability which is inclination independent. Our results independently confirm
that this \gamma-ray detected NLS1 harbors a $(2.8-7.9)\times10^6\,M_{\odot}$
BH similar to those in normal NLS1s rather than those in blazars.
