  We report the serendipitous discovery of a transient X-ray source, Suzaku
J1305$-$4930, $\sim$3 kpc southwest of the nucleus of the Seyfert 2 galaxy NGC
4945. Among the seven Suzaku observations of NGC 4945 from 2005 to 2011, Suzaku
J1305$-$4930 was detected four times in July and August in 2010. The X-ray
spectra are better approximated with a multi-color disk model than a power-law
model. At the first detection on 2010 July 4--5, its X-ray luminosity was
$(8.9^{+0.2}_{-0.4}) \times 10^{38}$ erg s$^{-1}$ and the temperature at the
inner-disk radius ($kT_{\rm in}$) was $1.12\pm0.04$ keV. At the last detection
with Suzaku on 2010 August 4--5, the luminosity decreased to
$(2.2^{+0.3}_{-0.8}) \times10^{38}$ erg s$^{-1}$ and $kT_{\rm in}$ was
$0.62\pm0.07$ keV. The source was not detected on 2011 January 29, about six
months after the first detection, with a luminosity upper limit of
$2.4\times10^{38}$ erg s$^{-1}$. We also find an absorption feature which is
similar to that reported in Cyg X-1. Assuming the standard disk, we suggest
that Suzaku J1305$-$4930 consists of a black hole with a mass of $\sim$10
$M_{\odot}$. The relation between the disk luminosity and $kT_{\rm in}$ is not
reproduced with the standard model of a constant inner radius but is better
approximated with a slim-disk model.
