  An efficient Monte Carlo method is extended to evaluate directly domain-wall
free-energy for randomly frustrated spin systems. Using the method, critical
phenomena of spin-glass phase transition is investigated in 4d +/-J Ising model
under the replica boundary condition. Our values of the critical temperature
and exponent, obtained by finite-size scaling, are in good agreement with those
of the standard MC and the series expansion studies. In addition, two
exponents, the stiffness exponent and the fractal dimension of the domain wall,
which characterize the ordered phase, are obtained. The latter value is larger
than d-1, indicating that the domain wall is really rough in the 4d Ising spin
glass phase.
