  A Wilsonian renormalization group (WRG) equation for nuclear current
operators in two-nucleon systems is derived. Nuclear current operators relevant
to low-energy Gamow-Teller transitions are analyzed using the WRG equation. We
employ the axial two-body current operators from phenomenological models and
heavy-baryon chiral perturbation theory, which are quite different from one
another in describing small scale physics. After reducing the model space of
the operators using the WRG equation, we find that there still remains a
significant model dependence at \Lambda = 200 MeV, where \Lambda is the sharp
cutoff specifying the size of the model space. A model independent effective
current operator is found at a rather small cutoff value, \Lambda = 70 MeV. By
simulating the effective current operator at \Lambda=70 MeV, we obtain a
current operator based on a pionless theory, thereby arguing an equivalence
relation between nuclear current operators of phenomenological models and those
of effective field theories.
