  We study the dynamics of topological defects in the context of ``topological
inflation" proposed by Vilenkin and Linde independently. Analysing the time
evolution of planar domain walls and of global monopoles, we find that the
defects undergo inflationary expansion if $\eta\stackrel{>}{\sim}0.33m_{Pl}$,
where $\eta$ is the vacuum expectation value of the Higgs field and $m_{Pl}$ is
the Planck mass. This result confirms the estimates by Vilenkin and Linde. The
critical value of $\eta$ is independent of the coupling constant $\lambda$ and
the initial size of the defect. Even for defects with an initial size much
greater than the horizon scale, inflation does not occur at all if $\eta$ is
smaller than the critical value. We also examine the effect of gauge fields for
static monopole solutions and find that the spacetime with a gauge monopole has
an attractive nature, contrary to the spacetime with a global monopole. It
suggests that gauge fields affect the onset of inflation.
