  An exact solution of domain wall junction is obtained in a four-dimensional
N=1 supersymmetric U(1) X U(1)' gauge theory with three pairs of chiral
superfields which is motivated by the N=2 SU(2) gauge theory with one flavor
perturbed by an adjoint scalar mass. The solution allows us to evaluate various
quantities including a new central charge Y_k associated with the junction
besides Z_k which appears already in domain walls. We find that the new central
charge Y_k gives a negative contribution to the mass of the domain wall
junction whereas the central charge Z_k gives a dominant positive contribution.
One has to be cautious to identify the central charge Y_k alone as the mass of
the junction.
