  Monitor of all-sky image (MAXI) Gas Slit Camera (GSC) detects gamma-ray
bursts (GRBs) including the bursts with soft spectra, such as X-ray flashes
(XRFs). MAXI/GSC is sensitive to the energy range from 2 to 30 keV. This energy
range is lower than other currently operating instruments which is capable of
detecting GRBs. Since the beginning of the MAXI operation on August 15, 2009,
GSC observed 35 GRBs up to the middle of 2013. One third of them are also
observed by other satellites. The rest of them show a trend to have soft
spectra and low fluxes. Because of the contribution of those XRFs, the MAXI GRB
rate is about three times higher than those expected from the BATSE log N - log
P distribution. When we compare it to the observational results of the
Wide-field X-ray Monitor on the High Energy Transient Explorer 2, which covers
the the same energy range to that of MAXI/GSC, we find a possibility that many
of MAXI bursts are XRFs with Epeak lower than 20 keV. We discuss the source of
soft GRBs observed only by MAXI. The MAXI log N - log S distribution suggests
that the MAXI XRFs distribute in closer distance than hard GRBs. Since the
distributions of the hardness of galactic stellar flares and X-ray bursts
overlap with those of MAXI GRBs, we discuss a possibility of a confusion of
those galactic transients with the MAXI GRB samples.
