  We present the first measurement of the angle phi_3 of the unitarity triangle
using a binned model-independent Dalitz plot analysis technique of B->DK, D->Ks
pi+pi- decay chain. The method is based on the measurement of parameters
related to the strong phase of D->Ks pi+ pi- amplitude performed by the CLEO
collaboration. The analysis uses full data set of 772x10^6 BBbar pairs
collected by the Belle experiment at Upsilon(4S) resonance. We obtain phi3 =
(77.3^{+15.1}_{-14.9} +- 4.2 +- 4.3) degree and the suppressed amplitude ratio
rB = 0.145 +- 0.030 +- 0.011 +- 0.011. Here the first error is statistical, the
second is experimental systematic uncertainty, and the third is the error due
to precision of strong phase parameters obtained by CLEO. This result is
preliminary.
