We give a bosonization of the quantum affine superalgebra $U_q(widehat{sl}(N|1))$ for an arbitrary level $k in {bf C}$. The bosonization of level $k in {bf C}$ is completely different from those of level $k=1$. From this bosonization, we induce the W
akimoto realization whose character coincides with those of the Verma module. We give the screening that commute with $U_q(widehat{sl}(N|1))$. Using this screening, we propose the vertex operator that is the intertwiner among the Wakimoto realization and typical realization. We study non-vanishing property of the correlation function defined by a trace of the vertex operators.
