  Candidates compounds for new thermoelectric and superconducting materials,
which have narrow band gap and flat bands near band edges, were exhaustively
searched by a high-throughput first-principles calculation from an inorganic
materials database named AtomWork. We focused on AgIn$_{5}$Se$_{8}$ which has
high density of state near the Fermi level. AgIn$_{5}$Se$_{8}$ was successfully
synthesized as single crystals using a melt and slow cooling method. The
single-crystal X-ray diffraction analysis revealed the obtained crystal is high
quality without deficiencies. The valence states in AgIn$_{5}$Se$_{8}$ were
determined to be Ag1+, In3+ and Se2- in accordance with a formal charge by the
core level X-ray photoelectron spectroscopy analysis. The electrical resistance
was evaluated under high pressure using a diamond anvil cell with boron-doped
diamond electrodes. Although the sample was insulator with a resistance of
above 40 M{\Omega} at ambient pressure, the resistance markedly decreased with
increase of the pressure, and a pressure-induced superconducting transition was
discovered at 3.4 K under 52.5 GPa. The transition temperature increased up to
3.7 K under further pressure of 74.0 GPa.
