We calculate neutrino velocity, in a background gravitational field on the basis of the Weinberg-Salam model and the general theory of relativity. We get an unexpected result which apparently contradicts with the equivalence principle. The neutrino velocity is greater than the ordinary light velocity c for some background metrics. The origin of this effect is that the neutrino, being virtually a pair of e^--W^+ or ν-Z, gets a quantum field theoretical space-time extension and feels tidal force. We discuss the relation between our result and the macro-causality.