  Using an exact solution as a concrete example, Nambu-Goldstone modes on the
BPS domain wall junction are worked out for N=1 supersymmetric theories in four
dimensions. Their wave functions extend along the wall to infinity (not
localized) and are not normalizable. It is argued that this feature is a
generic phenomenon of Nambu-Goldstone modes on domain wall junctions in the
bulk flat space in any dimensions. We formulate mode equations and show that
fermion and boson with the same mass come in pairs except massless modes which
can appear singly, in accordance with unitary representations of (1, 0)
supersymmetry.
