  3XMM J031820.8-663034, first detected by ROSAT in NGC 1313, is one of a few
known transient ultraluminous X-ray sources (ULXs). In this paper, we present
decades of X-ray data of this source from ROSAT, XMM-Newton, Chandra and the
Neil Gehrels Swift Observatory. We find that its X-ray emission experienced
four outbursts since 1992, with a typical recurrent time $\sim$ 1800 days, an
outburst duration $\sim 240-300$ days, and a nearly constant peak X-ray
luminosity $\sim 1.5 \times 10^{39}$ erg/s. The upper limit of X-ray luminosity
at the quiescent state is $\sim 5.6 \times 10^{36}$ erg/s, and the total energy
radiated during one outburst is $\sim 10^{46}$ erg. The spectra at the high
luminosity states can be described with an absorbed disk black-body, and the
disk temperature increases with the X-ray luminosity. We compare its outburst
properties with other known transient ULXs including ESO 243-49 HLX-1. As its
peak luminosity only marginally puts it in the category of ULXs, we also
compare it with normal transient black hole binaries. Our results suggest that
the source is powered by an accreting massive stellar-mass black hole, and the
outbursts are triggered by the thermal-viscous instability.
