  We study the creation of a fundamental string between D4-branes at angles in
string theory. It is shown that $R(-1)^{F}$ part of the one-loop potential of
open string changes its sign due to the change of fermionic zero-mode vacua
when the branes cross each other. As a result the effective potential is
independent of the angles when supersymmetry is partially unbroken, and leads
to a consistent picture that a fundamental string is created in the process. We
also discuss the s-rule in the configuration. The same result is obtained from
the one-loop potential for the orthogonal D4-branes with non-zero field
strength. The result is also confirmed from the tension obtained by deforming
the Chern-Simons term on one D4-brane, which is induced by another tilted
D4-brane.
