  XSS J12270-4859 (J12270) is an enigmatic source of unknown nature. Previous
studies revealed that the source has unusual X-ray temporal characteristics,
including repetitive short-term flares followed by spectral hardening,
non-periodic dips, and dichotomy in activity; i.e. intervals filled with flares
and those without. Together with a power-law X-ray spectrum, it is suggested to
be a low-mass X-ray binary (LMXB). In order to better understand the object, we
present the results of our near-infrared (NIR) photometry and linear
polarimetry observations as well as X-ray spectroscopy observations, which
overlap with each other partially in time, taken respectively with the InfraRed
Survey Facility (IRSF) and the Rossi X-ray Timing Explorer (RXTE). We detected
several simultaneous NIR and X-ray flares for the first time. No significant
NIR polarization was obtained. We assembled data taken with IRSF, RXTE, Suzaku,
Swift, and other missions in the literature and compared the flare profile and
the spectral energy distribution (SED) with some representative high-energy
sources. Based on some similarities of the repetitive NIR and X-ray flaring
characteristics and the broad SED, we argue that J12270 is reminiscent of
microquasars with a synchrotron jet, which is at a very low luminosity state of
~1e-4 Eddington luminosity for a stellar mass black hole or neutron star at a
reference distance of 1 kpc.
