  Big bang of the Friedmann-Robertson-Walker (FRW)-brane universe is studied.
In contrast to the spacelike initial singularity of the usual FRW universe, the
initial singularity of the FRW-brane universe is point-like from the viewpoint
of causality including gravitational waves propagating in the bulk. Existence
of null singularities (seam singuralities) is also shown in the flat and open
FRW-brane universe models.
