  We searched for superflares on solar-type stars using Kepler data with 1 min
sampling in order to detect superflares with short duration. We found 187
superflares on 23 solar-type stars whose bolometric energy ranges from the
order of $10^{32}$ erg to $10^{36}$ erg. Some superflares show multiple peaks
with the peak separation of the order of $100$-$1000$ seconds which is
comparable to the periods of quasi-periodic pulsations in solar and stellar
flares. Using these new data combined with the results from the data with 30
min sampling, we found the occurrence frequency ($dN/dE$) of superflares as a
function of flare energy ($E$) shows the power-law distribution ($dN/dE \propto
E^{-\alpha}$) with $\alpha \sim -1.5$ for $10^{33}<E<10^{36}$ erg which is
consistent with the previous results. The average occurrence rate of
superflares with the energy of $10^{33}$ erg which is equivalent to X100 solar
flares is about once in 500-600 years. The upper limit of energy released by
superflares is basically comparable to a fraction of the magnetic energy stored
near starspots which is estimated from the photometry. We also found that the
duration of superflares ($\tau$) increases with the flare energy ($E$) as $\tau
\propto E^{0.39\pm 0.03}$. This can be explained if we assume the time-scale of
flares is determined by the Alfv$\acute{\rm e}$n time.
