  New physics effects through the direct CP violation and the decay rate change
are investigated in the semileptonic $D_{l4}$ decays, $D^\pm\to K\pi l^\pm
\nu$, by including a scalar-exchange interaction with a complex coupling. In
the decay process, we included various excited states as intermediate states
decaying to the final hadrons, $K+\pi$, and found that among the intermediate
states only the lowest state ($K^*$) is dominant and the other higher excited
states are negligible, contrary to the $B_{l4}$ decays. We also obtained
constraints on the new complex coupling within the multi-Higgs doublet model
and the scalar leptoquark models.
