  We consider a possibility to naturally explain tiny neutrino masses without
the lepton number violation. We study a simple model with SU(2)_L singlet
charged scalars (s_1^+, s_2^+) as well as singlet right-handed neutrino (nu_R).
Yukawa interactions for Dirac neutrinos, which are forbidden at the tree level
by a softly-broken Z_2 symmetry, are induced at the one-loop level via the
soft-breaking term in the scalar potential. Consequently neutrinos obtain small
Dirac masses after the electroweak symmetry breaking. It is found that
constrains from neutrino oscillation measurements and lepton flavor violation
search results (especially for mu to e gamma) can be satisfied. We study the
decay pattern of the singlet charged scalars, which could be tested at the LHC
and the ILC. We discuss possible extensions also, e.g. to introduce dark matter
candidate.
