  We present a preliminary measurement of the Standard Model CP violation
parameter $\sin 2\phi_1$ using the Belle detector. A $6.2~{\rm fb}^{-1}$ sample
of events produced by the KEKB asymmetric $e^+e^-$ collider operating at the
$\Upsilon(4S)$ resonance is used. We report a preliminary result of $$\sin
2\phi_1=0.45^{+0.43}_{-0.44}({\rm stat})^{+0.07}_{-0.09}({\rm syst}).$$
