  One of the current most-demanded experiments in neutrino physics is to
measure the last mixing angle theta_13. KASKA is an experiment to detect new
type of reactor neutrino oscillation and to measure sin^2 2theta_13 accurately
using the world's most powerful nuclear reactor complex; Kashiwazaki-Kariwa
nuclear power station. KASKA utilizes near and far detectors of identical
structure at nearly optimized baselines and underground depths to cancel most
of the systematics and reduce backgrounds. The expected sensitivity is sin^2
2theta_13~0.015, which is 10 times better sensitivity than the current upper
limit measured by CHOOZ reactor experiment. Extension of KASKA project has
potential to accurately measure other anti-nu_e oscillation parameters. Intense
and precisely known neutrino flux measured by the KASKA-theta_13 phase can be
used to pin down sin^2 2theta_12 at a baseline ~50km and to measure Dm^2_13 for
the first time at a baseline ~5km. This Letter of Intent describes physics
motivation, detector system and expected performance of the KASKA experiment.
