  A recent study shows that Hawking radiation of the massless scalar field does
not appear on the two-dimensional AdS$_2$ black hole background. We study this
issue by investigating absorption and reflection coefficients under dilaton
coupling with the matter field. If the scalar field does not couple to the
dilaton, then it is fully absorbed into the black hole without any outgoing
mode. On the other hand, once it couples to the dilaton field, the outgoing
mode of the massless scalar field exists and the nontrivial Hawking radiation
is obtained. Finally, we comment on this dilaton dependence of Hawking
radiation in connection with a three-dimensional black hole.
