  An enhanced binding of an $N$-particle system interacting through a scalar
bose field is investigated, where $N\geq 2$. It is not assumed that this system
has a ground state for a zero coupling. It is shown, however, that there exists
a ground state for a sufficiently large values of coupling constants. When the
coupling constant is sufficiently large, $N$ particles are bound to each other
by the scalar bose field, and are trapped by external potentials. Basic ideas
of the proofs in this paper are applications of a weak coupling limit and a
modified HVZ theorem.
