  The critical strength of a magnetic field required for the suppression of the
Richtmyer-Meshkov instability (RMI) is investigated numerically by using a
two-dimensional single-mode analysis. For the cases of MHD parallel shocks, the
RMI can be stabilized as a result of the extraction of vorticity from the
interface. A useful formula describing a critical condition for MHD RMI has
been introduced, and which is successfully confirmed by the direct numerical
simulations. The critical field strength is found to be largely depending on
the Mach number of the incident shock. If the shock is strong enough, even
low-$\beta$ plasmas can be subject to the growth of the RMI.
