  The bright radio source S5 0716+714, which is usually classified as a BL Lac
object, is one of the most intensively studied blazar. S5 0716+714 demonstrates
extremely peculiar properties, such as the shortest time-scale of optical and
polarimetric variations observed in blazars. In the given talk, we present the
results of 8-h polarimetric monitoring of S5 0716+714 with a $\sim70$-sec
resolution carried out using the 6-m telescope BTA of the SAO RAS. The
observation data analysis reveals the variability both in total and polarized
light on the 1.5-hour timescales that specifies the size of the unresolved
emitting region. The numerical model of polarization in jet with the helical
structure of the magnetic field is suggested, and fitting the model reveals a
magnetic field precession with a period of about 15 days.
