Time-averaged flow fields behind finite circular cylinders with aspect ratios from 1.25 to 10 placed on a ground plate in a uniform flow were determined at a Reynolds number of 3.7×10⁴ and influences of the aspect ratios on the wake structures have been presented. Three-dimensional velocity distributions from 1 to 20 diameters down-stream of the cylinders were measured using newly developed rotating yaw-meter system, from which the details of the wake flow fields behind the finite circular cylinders have been discussed. Streamlines and vortex lines were calculated from the velocity fields and the wake structures, such as the configurations of vortices in the wake and their changes in shapes with distance downstream, have been shown. Effects of the shapes of the cylinder top on the wake flows have been also examined using modified cylinders with a hemispherical fairing, circular pipes as well as flat plates.