  We report on recent results obtained by the above collaboration on the
collision processes involving three nucleons, where we pay particular attention
on the dynamical role of the pion. After discussing the case at intermediate
energies, where real pions can be produced and detected, we have considered the
case at lower energies, where the pions being exchanged are virtual. The study
has revealed the presence of some new pion-exchange mechanisms, which leads to
a new three-nucleon force of tensor structure. Recently, the effect of this
tensor three-nucleon force to the spin observables for neutron-deuteron
scattering at low energy has been analyzed, and will be briefly reviewed.
