  We reconsider the force-balance relation on an isolated vortex in the flux
flow state within the scheme of time-dependent-Ginzburg-Landau (TDGL) equation.
We define force on the vortex by the total force on superconducting electrons
in the region $S$ surrounding the vortex. We derive the local momentum balance
relation of superconducting electrons and then find the force-balance relation
on isolated vortex with taking account of the fact that the transport current
in charged superconductors are inherently spatially varying with the scale of
penetration depth $\lambda$. We also find that nature of the driving force is
hydrodynamic when $S$ is the disk with radius $R$ satisfying $\xi\ll R\ll
\lambda$ ($\xi$ is the coherence length) while the hydrodynamic and magnetic
parts contribute equally to the driving force for $\lambda \lesssim R$.
