  We investigate gauge dependence of a nonrelativistic boundstate formalism
used in contemporary calculations. It is known that the effective Hamiltonian
of the boundstate system depends on the choice of gauge. We obtain the gauge
transformation charge of the Hamiltonian, by which gauge independence of the
mass spectrum and gauge dependences of the boundstate wave functions are
dictated. We raise two questions of practical and physical interest, and
provide answers to them.
