  We investigate the Kaluza-Klein braneworld cosmology from the point of view
of observers on the brane. We first generalize the Shiromizu-Maeda-Sasaki (SMS)
equations to higher dimensions. As an application, we study a (4+n)-dimensional
brane with n dimensions compactified on the brane, in a (5+n)-dimensional bulk.
By assuming that the size of the internal space is static, that the bulk
energy-momentum tensor can be neglected, we determine the effect of the bulk
geometry on the Kaluza-Klein braneworld. Then we derive the effective Friedmann
equation on the brane. It turns out that the Friedmann equation explicitly
depends on the equation of state, in contrast to the braneworld in a
5-dimensional bulk spacetime. In particular, in a radiation-dominated era, the
effective Newton constant depends on the scale factor logarithmically. If we
include a pressureless matter on the brane, this dependence disappears after
the radiation-matter equality. This may be interpreted as stabilization of the
Newton constant by the matter on the brane. Our findings imply that the
Kaluza-Klein braneworld cosmology is quite different from the conventional
Kaluza-Klein cosmology even at low energy.
