  We introduce the concept of equivalence among Wilson actions. Applying the
concept to a real scalar theory on a euclidean space, we derive the exact
renormalization group transformation of K. G. Wilson, and give a simple proof
of universality of the critical exponents at any fixed point of the exact
renormalization group transformation. We also show how to reduce the original
formalism of Wilson to the simplified formalism by J. Polchinski.
