  We present the first measurement of the angle phi_3 of the Unitarity Triangle
using a model-independent Dalitz plot analysis of B->DK, D->KsPiPi decays. The
method uses an input measurements of the strong phase of the D->KsPiPi
amplitude from the CLEO collaboration. The result is based on the full data set
of 772x10^6 BBbar pairs collected by the Belle experiment at the Upsilon(4S)
resonance. We obtain phi_3 = (77.3^{+15.1}_{-14.9} +- 4.1 +- 4.3)^{\circ} and
the suppressed amplitude ratio r_B = 0.145 +- 0.030 +- 0.010 +- 0.011. Here the
first error is statistical, the second is the experimental systematic
uncertainty, and the third is the error due to the precision of the
strong-phase parameters obtained by CLEO.
