  In this paper, an electroweak model with massive neutrinos is proposed. The
symmetry of the model is $SU(2)_L \times U(1)_Y \times U(1)_M$. Because of the
mixing of neutrinos, the conversion of one lepton type to another is possible,
but many of those kind processes are of extremely small possibilities. The
total lepton-number conservation still holds in this model, so neutrinoless
double beta decay is prohibited. Though right-hand neutrinos are introduced
into the model, their coupling with matter fields is extremely small and
therefore they are much harder to be detected in experiments.
