  We present the result of near-infrared and optical observations of the BL Lac
object S5 0716$ + $714 carried out by the KANATA telescope. S5 0716$ + $714 has
both a long term high-amplitude variability and a short-term variability within
a night. The shortest variability (microvariability) time-scale is important
for understanding the geometry of jets and magnetic field, because it provides
a possible minimum size of variation sources. Here, we report the detection of
15-min variability in S5 0716$ + $714, which is one of the shortest time-scales
in optical and near-infrared variations observed in blazars. The detected
microvariation had an amplitude of $0.061{\pm}0.005$ mag in $V$ band and a blue
color of $\Delta(V-J)=-0.025{\pm}0.011$. Furthermore, we successfully detected
an unprecedented, short time-scale polarimetric variation which correlated with
the brightness change. We revealed that the microvariation had a specific
polarization component. The polarization degree of the variation component was
higher than that of the total flux. These results suggest that the
microvariability originated from a small and local region where the magnetic
field is aligned.
