Shigeo Koshitani and Naoko Kunugi Broue conjecture holds for principal 3-blocks with elementary abelian defect group of order 9 Abstract. In representation theory of finite groups, there is a well known and important conjecture due to M. Brou\'e. He has conjectured that, for any prime $p$, if a finite group $G$ has an abelian Sylow $p$-subgroup $P$, then the principal $p$-blocks of $G$ and of the normalizer $N_G(P)$ of $P$ in $G$ are derived equivalent. We prove in this paper that the Brou\'e conjecture holds for the principal 3-block of an arbitrary finite group $G$ with elementary abelian Sylow 3-subgroup $P$ of order 9, by using initiated works for the case that $G$ is simple, which are due to Puig, Okuyama, Waki, Miyachi and the authors. The result depends on the classification of finite simple groups.