  We show that experimental results for the masses and mixing of the neutrinos
can be understood naturally by a simple grand unification model of SU(5)
coupled to N=1 supergravity. No right-handed neutrinos are included. The
left-handed neutrinos receive Majorana masses through the couplings with a
Higgs boson of symmetric $\bf 15$ representation. Introducing $\bar{\bf 45}$
representation is optional for describing the masses of down-type quarks and
charged leptons.
