The characteristics of the trailing vortex systems generated behind the blades of a fan turbine (denoted here as discharged wake vortex) were elucidated through a simultaneous measurement of the three components of velocity of the impeller discharge stream. A conditional sampling technique was applied to extract the well developed vortex signals. Totally 373 vortex signals were sampled. It was found that in spite of the scale of the vortex core being small (about one fourth of the impeller blade width), its rotational and axial velocities reach equal to and higher than the blade tip velocity, respectively. From these results, it was estimated that the discharge velocity of the vortex core is 2.4 times the impeller mean discharge velocity and the kinetic energy carried by the vortex core per unit area is 14.5 times larger than that of the impeller discharge stream. These results demonstrate how much the vortex contributes not only to gas or liquid dispersion but also to mixing in the impeller region.