  We construct a phenomenological three-nucleon force (3NF) model that gives a
good description of polarization observables in elastic nucleon-deuteron
(N-$d$) scattering at a low energy together with a realistic nucleon-nucleon
force and a 3NF arising from the exchange of two pions. Parameters of the
model, which consists of spin-independent, spin-orbit, and tensor components,
are determined to reproduce the three-nucleon binding energy and polarization
observables in N-d scattering at 3 MeV. Predictions of the model 3NF on N-d
polarization observables at higher energies are examined, and effects of each
component on the observables are investigated.
