  The inflationary scenario for the brane world driven by the bulk inflaton is
proposed. The quantum fluctuations of the inflaton is calculated and compared
to those of the conventional 4-dimensional inflationary scenario. It is shown
that the deviation of the primordial spectrum of this model from that of the
conventional one is too small to be observed even if $AdS$ radius is very
large. Hence, it turns out that the inflation caused by the bulk inflaton is
viable in the context of brane world cosmology.
