We give a functional derivation of the Ward-Takahashi identity for Yang-Mills theory in the framework of the exact renormalizationn group. The identity realizes non-abelian gauge symmetry nontrivially despite the presence of a momentum cutoff. The cutoff deforms the gauge transformation by introducing composite operators. In our functional method, which is an extension of the method used in our previous work in QED, these composite operators are expressed in terms of the Wilson action that depends on both a UV cutoff and an IR. cutoff.