  We introduce a new model applying to the core-nucleus and two-neutron system.
The Faddeev equations of 6He-n-n and 8He-n-n systems for 8He and 10He are
solved, respectively. The potential of the subsystem in the model has been
determined to make a coupling both of the ground state and the excited one
inside the core nucleus. By a similar mechanism the three-nucleon system is
solved with the three-body force originating from an isobar excitation of the
nucleon. Inputting only the information of subsystem energy levels and widths
we get the coupling constants of rank 1 Yamaguchi potential between the core
nucleus and neutron. We calculate the Faddeev three-cluster equations to obtain
the low-lying energy levels of 8He and 10He. The 1- state of 10He, which has
not been detected yet in experiments, is located in the energy level between
the 0+ and 2+ states.
