  We report the first observation of a narrow charmmonium state produced in the
exclusive decay process B+->K+ pi+pi- J/psi. This state, which decays into
pi+pi-J/psi, has a mass of 3871.8+-0.7(stat)+-0.4(syst) MeV, which is very near
the M_D + M_D* mass threshold. The results are based on an analysis of 152M
BBbar events collected at the Upsilon(4S) resonance in the Belle detector at
the KEKB collider.
