The ISS-based CALET detector which is in operation since October 2015, can play an important
role in indirect search of Dark Matter by measuring the electron + positron cosmic-ray spectrum
in the TeV region for the first time directly. With its fine energy resolution $(\sim 2\%)$ and high
proton rejection ratio $(1 : 10^5)$, CALET has a capability to detect fine structures in $(e^+ + e^− )$ spectrum.
In this work, we have investigated CALET’s potential to discern between Dark Matter
decay and nearby pulsars as the origin of the Cosmic Ray positron excess observed by PAMELA
or AMS-02. A parametrization of the propagated electron and positron spectra is fitted to the
existing measurements, where either 3-body decay of Fermionic Dark Matter or pulsar assumed
responsible for the positron excess. Expected CALET data for Dark Matter decay models which
can explain the positron excess are calculated and analyzed. The signal from a particular 3-body
Dark Matter decay, which can explain the measurements from the AMS-02 experiment, is shown
to be distinguishable from a single pulsar source by observing $(e^+ + e^−)$ spectrum with CALET.
We show that an especially clear separation of the pulsar model is possible from the Dark Matter
model for which the diffuse γ-ray flux is possibly compatible with the Fermi-LAT data.