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Superflares are flares that release total energy 10$\sim$10$^{4}$ timesgreater than that of the biggest solar flares with energy of $\sim$10$^{32}$erg. We searched superflares on solar-type stars (G-type main sequence stars)using the Kepler 30-min (long) and 1-min (short) cadence data. We found morethan 1500 superflares on 279 stars from 30-min cadence data (Q0-6) and 187superflares on 23 stars from 1-min cadence data (Q0-17). The bolometric energyof detected superflares ranges from the order of 10$^{32}$ erg to 10$^{36}$erg. Using these data, we found that the occurrence frequency ($dN/dE$) ofsuperflares is expressed as a power-law function of flare energy ($E$) with theindex of -1.5 for $10^{33}<E<10^{36}$erg. Most of the superflare stars showquasi-periodic light variations with the amplitude of a few percent, which canbe explained by the rotation of the star with large starspots. The bolometricenergy released by flares is consistent with the magnetic energy stored aroundsuch large starspots. Furthermore, our analyses indicate that the occurrencefrequency of superflares depends on the rotation period, and that the flarefrequency increases as the rotation period decreases. However, the energy ofthe largest flares observed in a given period bin does not show any clearcorrelation with the rotation period. We also found that the duration ofsuperflares increases with the flare energy as $E^{0.39+/-0.03}$. This can beexplained if we assume the time-scale of flares is determined by theAlfv$\acute{\rm{e}}$n time.

Statistical properties of superflares on solar-type stars with Kepler data