  We theoretically study a non-magnetic impurity effect on the vortex bound
states of a multi-quantum vortex. The zero-energy peak of the local density of
states is investigated for vortex cores with the winding numbers 2 and 4 within
the framework of the quasiclassical theory of superconductivity. We find that
the zero-energy peaks, which appear away from the vortex center in the clean
limit, move towards the vortex center with increasing the impurity scattering
rate, resolving a contradiction between an experimental result and previous
theoretical predictions.
