  Super-Kamiokande collaboration assumes that the direction of every observed
lepton coincides with the incoming direction of the incident neutrino, which is
the fundamental basement throughout all their analysis on neutrino oscillation.
We examine whether this assumption to explain the experimental results on
neutrino oscillation is theoretically acceptable. Treating every physical
process concerned stochastically, we have examined if this assumption just
cited is acceptable. As the result of it, we have shown that this assumption
does not hold even if statistically.
