  We study the dependence of the number density and properties of quasars on
the background galaxy density using the currently largest spectroscopic
datasets of quasars and galaxies. We construct a galaxy number density field
smoothed over the variable smoothing scale of between approximately 10 and
$20\,h^{-1}$Mpc over the redshift range of $0.46<z<0.59$ using the Sloan
Digital Sky Survey (SDSS) Data Release 12 (DR12) Constant MASS (CMASS)
galaxies. The quasar sample is prepared from the SDSS I/II DR7. We examine the
correlation of incidence of quasars with the large-scale background density and
dependence of quasar properties such as bolometric luminosity, black hole mass,
and Eddington ratio on the large-scale density. We find a monotonic correlation
between the quasar number density and large-scale galaxy number density, which
is fitted well with a power law relation, $n_Q\propto\rho_G^{0.618}$. We detect
weak dependences of quasar properties on the large-scale density such as a
positive correlation between black hole mass and density, and a negative
correlation between luminosity and density. We discuss the possibility of using
quasars as a tracer of large-scale structures at high redshifts, which may be
useful for studies of growth of structures in the high redshift universe.
