  We discuss a supersymmetric extension of the standard model with an extra
U(1) gauge symmetry. In this model, the proton stability is guaranteed by the
gauge symmetry without invoking R parity. The gauge symmetry breakdown
automatically generates an effective $\mu$ term and large Majorana masses for
right-handed neutrinos. The supersymmetry-soft-breaking terms for scalar fields
could be universal at a very high energy scale, and the electroweak symmetry is
broken through radiative corrections.
