  We select blue-horizontal branch stars (BHBs) from the internal data release
of the Hyper Suprime-Cam Subaru Strategic Program to reveal the global
structure of the Milky Way (MW) stellar halo. The data are distributed over
$\sim 1,100$~deg$^2$ area in the range of $18.5<g<24.5$~mag, so that candidate
BHBs are detectable over a Galactocentric radius of $r \simeq 36-575$~kpc. In
order to select most likely BHBs by removing blue straggler stars and other
contaminants in a statistically significant manner, we develop and apply an
extensive Bayesian method, as described in \citet{Fukushima2019}. Our sample
can be fitted to either a single power-law profile with an index of
$\alpha=4.11^{+0.18}_{-0.18}$ or a broken power-law profile with an index of
$\alpha_{\rm in}=3.90^{+0.24}_{-0.30}$ at $r$ below a broken radius of $r_{\rm
b}=184^{+118}_{-66}$ kpc and a very steep slope of $\alpha_{\rm
out}=9.1^{+6.8}_{-3.6}$ at $r>r_{\rm b}$; the statistical difference between
these fitting profiles is small. Both profiles are found to show prolate shapes
having axial ratios of $q=1.47^{+0.30}_{-0.33}$ and $1.56^{+0.34}_{-0.23}$,
respectively. We also find a signature of the so-called "splashback radius" for
the candidate BHBs, which can reach as large as $r \sim 575$~kpc, although it
is still inconclusive owing to rather large distance errors in this faintest
end of the sample. Our results suggest that the MW stellar halo consists of the
two overlapping components: the {\it in situ} inner halo showing a relatively
steep radial density profile and the {\it ex situ} outer halo with a shallower
profile, being characteristic of a component formed from accretion of small
stellar systems.
