This study is to clarify the flow structure of a three-dimensional wall jet discharged on a flat surface from a circular nozzle. Mean velocities and fluctuating velocities in a cross section of a fully-developed flow region were measured by using a rotating single hot-wire probe. The direction of the mean flow in the inner layer is about constant and coincides with the radial lines from a virtual origin of jet. The distributions of the mean velocity in the normal direction to the wall are almost similar to each other in the inner scaling. Skin friction coefficients were estimated by means of the momentum balance analysis.