  Recent detection of gravitational waves from a neutron star (NS) merger event
GW170817 and identification of an electromagnetic counterpart provide a unique
opportunity to study the physical processes in NS mergers. To derive properties
of ejected material from the NS merger, we perform radiative transfer
simulations of kilonova, optical and near-infrared emissions powered by
radioactive decays of r-process nuclei synthesized in the merger. We find that
the observed near-infrared emission lasting for > 10 days is explained by 0.03
Msun of ejecta containing lanthanide elements. However, the blue optical
component observed at the initial phases requires an ejecta component with a
relatively high electron fraction (Ye). We show that both optical and
near-infrared emissions are simultaneously reproduced by the ejecta with a
medium Ye of ~ 0.25. We suggest that a dominant component powering the emission
is post-merger ejecta, which exhibits that mass ejection after the first
dynamical ejection is quite efficient. Our results indicate that NS mergers
synthesize a wide range of r-process elements and strengthen the hypothesis
that NS mergers are the origin of r-process elements in the Universe.
