  Sensitivities to sin^2{2theta_{13}} without statistical errors (``systematic
limit'') are investigated in neutrino oscillation experiments with multiple
reactors. Using an analytical approach, we show that the systematic limit on
sin^2{2theta_{13}} is dominated by the uncorrelated systematic error sigma_u of
the detector. Even in an experiment with multi-detectors and multi-reactors, it
turns out that most of the systematic errors including the one due to the
nature of multiple sources is canceled as in the case with a single reactor
plus two detectors, if the near detectors are placed suitably. The case of the
KASKA plan (7 reactors and 3 detectors) is investigated in detail, and it is
explicitly shown that it does not suffer from the extra uncertainty due to
multiple reactors.
