This paper considers the active power flow control of a distributed-parameter planar structure, with particular emphasis on a vortex power flow which has the potential to confine the vibrational power into a restricted area of the structure. Without letting the vibrational power, a cause of exciting structural modes, disperse into the structure, control of the structural response can be achieved. This paper begins by deriving the necessary condition for producing a vortex power flow in the vicinity of a disturbance point force at an arbitrary exciting frequency. Then, with a wave visualization system newly developed, it becomes possible to observe the wave propagation (the vortex power flow) taking place in the structure. In order to investigate the contribution of structural modes to the vortex power flow configuration, an energy stream function as well as a vorticity function is derived in a general form. By using these functions, the generation mechanism of a vortex power flow actively induced around a disturbance force location is quantitatively studied.