  The mobility of the Wigner solid on the superfluid $^3$He is determined by
the momentum transfer from the scattered $^3$He quasiparticles at the free
surface. The scattering process of the quasiparticles is classified into the
normal reflection and the Andreev retroreflection. Since the quasiparticles
nearly conserve the momentum in the process of the Andreev retroreflection at
the free surface, the Andreev reflected quasiparticles do not produce a
resistive force to the Wigner solid. In this report, we have analytically
calculated the contribution of the Andreev retroreflection to the mobility of
the Wigner solid on superfluid $^3$He-B by employing a realistic model order
parameter with the free surface. The Andreev retroreflection is lacked for
quasiparticles with energy above the bulk energy gap under the model order
parameter. Then, the Andreev retroreflection does not contribute to a rise in
the mobility of the Wigner solid on the superfluid $^3$He-B. The present model
calculation is in good agreement with the previous experimental observation. We
have also discussed the Andreev retroreflection under a self-consistently
calculated order parameter.
