  Supersymmetric effective potential of a 5D super-Yang-Mills model
compactified on $S^1/Z_2$, i.e., on an interval $l$ of extra dimension, is
estimated at the 1-loop level by the auxiliary field tadpole method. For the
sake of infinite towers of Kaluza-Klein excitation modes of bulk fields
involved in the tadpoles, there arises a definite bulk effect of linear growth
of the effective potential along with the cutoff ${\mit\Lambda}$ which is
greatly suppressed by $l$ to produce finite contributions. The minimization of
the effective potential incorporating the tree potential and a Fayet-Iliopoulos
$D$-term reveals an interesting case that the size of $l$ is stabilized at a
length corresponding to an intermediate mass scale $10^{12-14}$ GeV.
