  We measure the evolution of the $M_{\rm BH}-M_*$ relation using 584
uniformly-selected SDSS quasars at $0.2<z<0.8$. The black-hole masses ($M_{\rm
BH}$) are derived from the single-epoch virial mass estimator using the
H$\beta$ emission line, and span the range $7.0<{\rm log}\,M_{\rm
BH}/M_\odot<9.5$. The host-galaxy stellar masses ($M_*$), which cover the
interval $10.0<{\rm log}\,M_* / M_\odot <11.5$, are determined by performing
two-dimensional quasar-host decomposition of the Hyper Suprime-Cam images and
spectral energy distribution fitting. To quantify sample-selection biases and
measurement uncertainties on the mass terms, a mock quasar sample is
constructed to jointly constrain the redshift evolution of the $M_{\rm BH}-M_*$
relation and its intrinsic scatter ($\sigma_\mu$) through forward modeling. We
find that the level of evolution is degenerate with $\sigma_\mu$, such that
both positive mild evolution (i.e, $M_{\rm BH}/M_*$ increases with redshift)
with a small $\sigma_\mu$, and negative mild evolution with a larger
$\sigma_\mu$ are consistent with our data. The posterior distribution of
$\sigma_\mu$ enables us to put a strong constraint on the intrinsic scatter of
the $M_{\rm BH}-M_*$ relation, which has a best inference of
$0.25_{-0.04}^{+0.03}$ dex, consistent with the local value. The redshift
evolution of the $M_{\rm BH}-M_*$ relation relative to the local relation is
constrained to be $(1+z)^{0.12_{-0.27}^{+0.28}}$, in agreement with no
significant evolution since $z\sim0.8$. The tight and non-evolving $M_{\rm
BH}-M_*$ relation is suggestive of a coupling through AGN feedback or/and a
common gas supply at work, thus restricting the mass ratio of galaxies and
their black holes to a limited range. Given the considerable stellar disk
component, the $M_{\rm BH}-M_{\rm bulge}$ relation may evolve as previously
seen at higher redshifts.
