  This study presents multi-wavelength observational results for energetic
GRB100414A with GeV photons. The prompt spectral fitting using Suzaku/WAM data
yielded spectral peak energies of E^src_peak of 1458.7 (+132.6, -106.6) keV and
Eiso of 34.5(+2.0, -1.8) x 10^52 erg with z=1.368. The optical afterglow light
curves between 3 and 7 days were effectively fitted according to a simple power
law with a temporal index of alpha=-2.6 +/- 0.1. The joint light curve with
earlier Swift/UVOT observations yields a temporal break at 2.3 +/- 0.2 days.
This was the first \fermi/LAT detected event that demonstrated the clear
temporal break in the optical afterglow. The jet opening angle derived from
this temporal break was 5.8 degree, consistent with those of other
well-observed long gamma-ray bursts (GRBs). The multi-wavelength analyses in
this study showed that GRB100414A follows E^src_peak-Eiso and
E^src_peak-E_gamma correlations. The late afterglow revealed a flatter
evolution with significant excesses at 27.2 days. The most straightforward
explanation for the excess is that GRB100414A was accompanied by a
contemporaneous supernova. The model light curve based on other GRB-SN events
is marginally consistent with that of the observed lightcurve.
