Three-dimensional numerical computations have been performed in order to investigate the mixing mechanism of a multi-holed (composed of two pairs of 4- and 5-hole elements) static mixer for Newtonian fluid. The hole Reynolds number based on the size ofstraight part of the hole and the mean velocity in a hole of the 5-hole element, Rea, was changed in three steps from 5.25 to 52.7, while the hole size of the straight part of the bole, the pipe diameter and fluid viscosity and density were fixed at 5 mm, 18 mm, and 0.0978 Pa.s and 1304 kg.m(-3), respectively, which were the same as in the previous experiments. From the results, it was found that twin vortices are formed in a hole of the 5-hole element as observed experimentally in the previous study. These twin vortices cause the twist motion in a hole and intensify the mixing process of the static mixer. It was also found that the vorticity of the twin vortices linearly increases with the hole Reynolds number. Thus, the increase of the hole Reynolds number causes high mixing characteristics as pointed out in the previous study.