  We demonstrate enormous power of dedicated reactor experiment for \theta_{12}
with a detector placed at around the first oscillation maximum, which we call
"SADO". It allows determination of sin^2\theta_{12} to the accuracy of \simeq
2% at 1 \sigma CL, which surpasses all the method so far proposed. Unlike
reactor \theta_{13} experiments, the requirement for the systematic error is
very mild, \simeq 4%, which makes it an even more feasible experiment. If we
place a detector at \sim 60 km away from the Kashiwazaki-Kariwa nuclear power
plant, 0.5 kt yr exposure of SADO is equivalent to \sim 100 kt yr exposure of
KamLAND assuming the same systematic error.
