tJsing functional analysis technigues, it is shown that the functional eguation f(Z + W;) — (3 f(z) = g(z) always has a solution in the spaces (p) and r(p_(P,T) to which g helongs. ît is also sh.own that these spaces are Montel. The results of this paper generalize the corres- ponding results of Whittaker [10], Scott [8] and Krishnamurthy [5j. 1. Whıttaker’s [10] classical theorem States that for any entire function g of order p tkere existg such. that the eguation an entire function f of the same order