  We have searched for a T/CP violation signature arising from an electric
dipole form factor (d_tau) of the tau lepton in the e+e- -> tau+tau- reaction.
Using an optimal observable method for 29.5 fb^{-1} of data collected with the
Belle detector at the KEKB collider at sqrt{s}=10.58 GeV, we obtained the
preliminary result Re(d_tau) = (1.15 +- 1.70) x 10^{-17} ecm and Im(d_tau) =
(-0.83 +- 0.86) x 10^{-17} ecm for the real and imaginary parts of d_tau,
respectively, and set the 95% confidence level limits -2.2 < Re(d_tau) < 4.5
(10^{-17} ecm) and -2.5 < Im(d_tau) < 0.8 (10^{-17} ecm).
