  Fast radio bursts (FRBs) at cosmological distances have recently been
discovered, whose duration is about milliseconds. We argue that the observed
short duration is difficult to explain by giant flares of soft gamma-ray
repeaters, though their event rate and energetics are consistent with FRBs.
Here we discuss binary neutron star (NS-NS) mergers as a possible origin of
FRBs. The FRB rate is within the plausible range of NS-NS merger rate and its
cosmological evolution, while a large fraction of NS-NS mergers must produce
observable FRBs. A likely radiation mechanism is coherent radio emission like
radio pulsars, by magnetic braking when magnetic fields of neutron stars are
synchronized to binary rotation at the time of coalescence. Magnetic fields of
the standard strength (~ 10^{12-13} G) can explain the observed FRB fluxes, if
the conversion efficiency from magnetic braking energy loss to radio emission
is similar to that of isolated radio pulsars. Corresponding gamma-ray emission
is difficult to detect by current or past gamma-ray burst satellites. Since
FRBs tell us the exact time of mergers, a correlated search would significantly
improve the effective sensitivity of gravitational wave detectors.
