  We investigate the heavy quark mass effects on the parton distribution
functions in the unpolarized virtual photon up to the next-to-leading order in
QCD. Our formalism is based on the QCD-improved parton model described by the
DGLAP evolution equation as well as on the operator product expansion
supplemented by the mass-independent renormalization group method. We evaluate
the various components of the parton distributions inside the virtual photon
with the massive quark effects, which are included through the initial
condition for the heavy quark distributions, or equivalently from the matrix
element of the heavy quark operators. We discuss some features of our results
for the heavy quark effects and their factorization-scheme dependence.
