  The recently reported diphoton excess at the LHC may imply the existence of a
new resonance with a mass of about 750 GeV which couples to photons via loops
of new charged particles. In this letter, we study the possibility to test such
models at the ILC, paying attention to the new charged particles responsible
for the diphoton decay of the resonance. We show that they affect the
scattering processes $e^+e^- \to f\bar{f}$ (with $f$ denoting Standard Model
fermions) at the ILC, which makes it possible to indirectly probe the new
charged particles even if they are out of the kinematical reach. We also show
that the discriminations of the diphoton models may be possible based on a
study of the angular distributions of $f\bar{f}$.
