  Recently, many superflares on solar-type stars have been discovered as
white-light flares (WLFs). The statistical study found a correlation between
their energies ($E$) and durations ($\tau$): $\tau \propto E^{0.39}$ (Maehara
et al. 2017 $EP\& S$, 67, 59), similar to those of solar hard/soft X-ray
flares: $\tau \propto E^{0.2-0.33}$. This indicates a universal mechanism of
energy release on solar and stellar flares, i.e., magnetic reconnection. We
here carried out a statistical research on 50 solar WLFs observed with
\textit{SDO}/HMI and examined the correlation between the energies and
durations. As a result, the $E$--$\tau$ relation on solar WLFs ($\tau \propto
E^{0.38}$) is quite similar to that on stellar superflares ($\tau \propto
E^{0.39}$). However, the durations of stellar superflares are one order of
magnitude shorter than those expected from solar WLFs. We present the following
two interpretations for the discrepancy. (1) In solar flares, the cooling
timescale of WLFs may be longer than the reconnection one, and the decay time
of solar WLFs can be elongated by the cooling effect. (2) The distribution can
be understood by applying a scaling law ($\tau \propto E^{1/3}B^{-5/3}$)
derived from the magnetic reconnection theory. In this case, the observed
superflares are expected to have 2-4 times stronger magnetic field strength
than solar flares.
