  Photon structure functions in supersymmetric QCD are investigated in terms of
the parton model where squark contributions are evaluated. We calculate the
eight virtual photon structure functions by taking the discontinuity of the
squark massive one-loop diagrams of the photon-photon forward amplitude. The
model-independent positivity constraints derived from the Cauchy-Schwarz
inequalities are satisfied by the squark parton model calculation and actually
the two equality relations hold for the squark contribution. We also show that
our polarized photon structure function $g_1^\gamma$ for the real photon leads
to the vanishing 1st moment sum rule, and the constraint $|g_1^\gamma|\leq
F_1^\gamma$ is satisfied by the real photon. We also discuss a squark signature
in the structure function $W_{TT}^\tau$.
