We have discovered 1547 ‘superflares’ on about 279 G-type main-sequence stars by using the Kepler-spacecraft data of Q0-Q6. ‘Superflares’ mean flares that radiate total energy 10 times or more larger than that of the largest flare in the Sun ever recorded. We here briefly review our current understandings on superflares and superflare stars obtained by analyzing the Kepler data and follow-up high dispersion spectra.