We investigate a balance network of the asymmetric simple exclusion process
(ASEP). Subsystems consisting of ASEPs are connected by bidirectional links
with each other, which results in balance between every pair of subsystems. The
network includes some specific important cases discussed in earlier works such
as the ASEP with the Langmuir kinetics, multiple lanes and finite reservoirs.
Probability distributions of particles in the steady state are exactly given in
factorized forms according to their balance properties. Although the system has
nonequilibrium parts, the expressions are well described in a framework of
statistical mechanics based on equilibrium states. Moreover, the overall
argument does not depend on the network structures, and the knowledge obtained
in this work is applicable to a broad range of problems