  We study the modification of the chiral phase structure of QCD due to an
external magnetic field. We first demonstrate how the effect of magnetic field
can systematically be incorporated into a generalized Ginzburg-Landau
framework. We then analyze the phase structure in the vicinity of the chiral
critical point. In the chiral limit, the effect is found to be so drastic that
it totally washes the tricritical point out of the phase diagram, bringing the
continent for the chiral spiral. This is the case no matter how small is the
intensity of the magnetic field. On the other hand, the current quark mass
protects the chiral critical point from a weak magnetic field. However the
critical point will eventually be covered by the chiral spiral phase as the
magnetic field grows.
