  We estimate the strength of large-scale magnetic fields produced during
inflation in the framework of Dirac-Born-Infeld (DBI) theories. This analysis
is sufficiently general in the sense that it covers most of conformal symmetry
breaking theories in which the electromagnetic field is coupled to a scalar
field. In DBI theories there is an additional factor associated with the speed
of sound, which allows a possibility to lead to an extra amplification of the
magnetic field in a ultra-relativistic region. We clarify the conditions under
which seed magnetic fields to feed the galactic dynamo mechanism at a
decoupling epoch as well as present magnetic fields on galactic scales are
sufficiently generated to satisfy observational bounds.
