  We created a three-dimensional distribution map of molecular gas throughout
the Milky Way Galaxy using the latest $^{12}$CO($J=$1--0) survey data cube and
rotation curve based on the kinematic distance. The radial distribution of the
molecular gas shows a central peak and a second peak around 0.5 $R_0$. The
thickness of the molecular disk slightly increases from 48 pc to 160 pc with
the galactocentric distance within a radius range of 0--11 kpc. We were able to
trace the Outer, the Perseus, the Sagittarius-Carina, the Scutum-Crux, and the
Norma arms as logarithmic spiral arms with pitch angles of $11\arcdeg -
15\arcdeg$. Considering that the pitch angles of the spiral arms are within
this range, the Norma and the Outer arms {seem to} be identified as the same
spiral arm. We could also trace a midplane displacement, whose amplitude is
nearly constant inside a 10 kpc radius and increases beyond this radius. The
ridges of midplane displacement form leading spiral arms.
