  We study phases and fractal structures of three-dimensional simplicial
quantum gravity by the Monte-Carlo method. After measuring the surface area
distribution (SAD) which is the three-dimensional analog of the loop length
distribution (LLD) in two-dimensional quantum gravity, we classify the fractal
structures into three types: (i) in the hot (strong coupling) phase, strong
gravity makes the space-time one crumpled mother universe with small
fluctuating branches around it. This is a crumpled phase with a large Hausdorff
dimension $d_{\mbox{\tiny H}} \simeq 5$. The topologies of cross-sections are
extremely complicated. (ii) at the critical point, we observe that the
space-time is a fractal-like manifold which has one mother universe with small
and middle size branches around it. The Hausdorff dimension is $d_{\mbox{\tiny
H}} \simeq 4$. We observe some scaling behaviors for the cross-sections of the
manifold. This manifold resembles the fractal surface observed in
two-dimensional quantum gravity. (iii) in the cold (weak coupling) phase, the
mother universe disappears completely and the space-time seems to be the
branched-polymer with a small Hausdorff dimension $d_{\mbox{\tiny H}} \simeq
2$. Almost all of the cross-sections have the spherical topology $S^2$ in the
cold phase.
