In molten equivalent salts, a unified relation that the ratio of partial dc conductivities is always equal to the inverse mass ratio, viz. sigma(+)/sigma(-)=m(-)/m(+), has been confirmed in view of microscopic point starting from the generalized Langevin equation. It has been newly proved that the memory functions assumed to be an exponentially decaying form in the Langevin equation for cation and anion are equal to each other. Furthermore, the short time behaviors of moving ions are analyzed in terms of their velocity correlation functions, according to the combination of generalized Langevin equation and damped Einstein oscillator equation. A minor correction for the expression of common friction constant derived before has been given. Estimated results for conductivities are close to those obtained by computer simulation and also comparable to experimental values. (C) 2004 American Institute of Physics.