  We study the current structure of the lepton flavor violating $\tau\to3\mu$
decay in Type-III 2HDM. This model has many coupling constants which affect
this decay. We find that each coupling constant corresponds to the different
final-state momenta distribution and vice versa. Using this fact, we suggest
how to determine the current structure. We also find the upper limit
$|\eta_{23}^E\eta_{22}^E|<0.00022$ in the case that all Higgs bosons except for
the lighter CP even neutral one $h^0$ are decoupled, $M_{h^0}=115$GeV and
$\cos\beta=1/\sqrt{2}$. The observable difference between the MSSM and type-III
2HDM is also discussed.
