  We present optical multi-colour photometry of V404 Cyg during the outburst
from December, 2015 to January, 2016 together with the simultaneous X-ray data.
This outburst occurred less than 6 months after the previous outburst in
June-July, 2015. These two outbursts in 2015 were of a slow rise and rapid
decay-type and showed large-amplitude ($\sim$2 mag) and short-term ($\sim$10
min-3 hours) optical variations even at low luminosity (0.01-0.1$L_{\rm Edd}$).
We found correlated optical and X-ray variations in two $\sim$1 hour time
intervals and performed Bayesian time delay estimations between them. In the
previous version, the observation times of X-ray light curves were measured at
the satellite and their system of times was Terrestrial Time (TT), while those
of optical light curves were measured at the Earth and their system of times
was Coordinated Universal Time (UTC). In this version, we have corrected the
observation times and obtained a Bayesian estimate of an optical delay against
the X-ray emission, which is $\sim$30 s, during those two intervals. In
addition, the relationship between the optical and X-ray luminosity was $L_{\rm
opt} \propto L_{\rm X}^{0.25-0.29}$ at that time. These features can be
naturally explained by disc reprocessing.
