  We study a rate asymmetry in the inclusive decay $\Bsgamma$, assuming the
supersymmetric standard model based on N=1 supergravity. A complex coefficient
$A$ for scalar-trilinear couplings is the source of CP violation, which is
contained in the mass-squared matrices for squarks. The model parameters are
nontrivially constrained by experimental results for the branching ratio of the
radiative decay and for the electric dipole moments of the neutron and the
electron. The decay rate asymmetry is predicted to be much larger than that by
the standard model in a wide region of the parameter space compatible with the
experiments. Its magnitude can be maximally around 0.1, which will be well
accessible at B factories.
