  The KEK to Kamioka long-baseline neutrino experiment (K2K) is the first
accelerator-based experiment with hundreds of km neutrino path length. K2K
focuses on the study of the existence of neutrino oscillations in $\nu_{\mu}$
disappearance that is observed in atmospheric neutrinos. With nearly pure muon
neutrino beam produced with $5.6\times 10^{19}$ protons from 12 GeV PS on
target, 56 neutrino events have been observed at Super-Kamiokande, the far
detector at 250 km distance. The expectation is $80.6^{+7.3}_{-8.0}$ derived
from the measurement at the near site. The experiment expects to accumulate
$10^{20}$ protons on target, providing sufficient statistics to study neutrino
oscillations by spectral analysis for $\nu_{\mu}$ disappearance.
