A magnetic divertor is introduced to the HIEI tandem mirror to enhance the MHD stability in axisymmetric magnetic configuration. It is confirmed that the MHD flute modes can be stabilized by the divertor located at the midplane or off-midplane in the central cell. As the position of the magnetic nulls of the divertor is located at smaller radii, the plasma can be sustained with less fueling rates. The magnetic divertor provides a method to greatly enhance the stability of the flute modes for plasmas weakly stabilized by the RF ponderomotive force.