  We discuss ways to explore non-standard interactions (NSI) which neutrinos
may possess by expressing them as effective four Fermi operators with
coefficient of the order of (M_{W} / M_{NP})^2 ~0.01 (0.0001) for energy scales
of new physics as M_{NP} ~1 (10) TeV. Neutrino Factory is a prime candidate for
such apparatus that can reach to the extreme precision. I describe a two
detector setting, one at baseline L~3000 km and the other at L~7000 km, which
is able to solve the notorious theta_{13}-NSI confusion, and possibly also the
two-phase confusion. The resultant sensitivities to off-diagonal NSI elements
\epsilon's are excellent, |\epsilon_{e tau}| \simeq a few \times10^{-3} and
|\epsilon_{e mu}| \simeq a few \times10^{-4}. Our results suggest a new picture
of neutrino factory as a hunting machine for NSI while keeping its potential of
precision measurement of lepton mixing parameters. Sensitivities to NSI by T2KK
and the related settings are also discussed.
