  We obtain a new constraint on the CP-violating flavor mixing between the
left-handed top scalar quark (\tilde{t}_L) and charm scalar quark
(\tilde{c}_L), by considering a chargino loop contribution to chromo-electric
dipole moment of strange quark, which is limited by the electric dipole moment
of the neutron and atoms. It is found that the flavor mixing should be
suppressed to the level of {\cal O}(0.1) for the CP phase of order unity.
Although it is much stronger than the known constraint from the chargino loop
contribution to b \to s \gamma, the moderate constraint we obtain here is
argued to leave room for sizable supersymmetric contribution to the CP
asymmetry in B_d^0 \to \phi K^0.
