  We present the results of timing analysis of the XMM-Newton observation of
the Seyfert 2 galaxy NGC 6300. The hard X-ray spectrum above 2 keV consists of
a Compton-thin-absorbed power law, as is often seen in Seyfert 2 galaxies. We
clearly detected rapid time variability on a time scale of about 1000 s from
the light curve above 2 keV. The excess variance of the time variability
(sigma2_RMS) is calculated to be ~0.12, and the periodogram of the light curve
is well represented by a power law function with a slope of 1.75. In contrast
with previous results from Seyfert 2 nuclei, these variability characteristics
are consistent with those of Seyfert 1 galaxies. This consistency suggests that
NGC 6300 has a similar black hole mass and accretion properties as Seyfert 1
galaxies. Using the relation between time variability and central black hole
mass by Hayashida et al. (1998), the black hole mass of NGC 6300 is estimated
to be ~2.8x10^5 Mo. Taking uncertainty of this method into account, the black
hole mass is less than 10^7 Mo. Taking the bolometric luminosity of 3.3x10^43
erg/s into consideration, this yields an accretion rate of > 0.03 of the
Eddington value, and comparable with estimates from Seyfert 1 galaxies using
this method. The time variability analysis suggests that NGC 6300 actually has
a Seyfert 1 nucleus obscured by a thick matter, and more generally provides a
new pillar of support for the unified model of Seyfert galaxies based on
obscuration.
