A water wheel impeller blade type electric power generating apparatus with which, on the forward motion side, the hydraulic pressure applied to the impeller blade is reduces, and the mud, sand, dirt, and the like will not be collected into the water wheel. The impeller blade is rotatably disposed on the rotor, and has a stopper part and a fluid receiving part extending from this stopper part and being longer than the stopper part, the fluid receiving part being provided with a length large enough that when the impeller blade is thrust down the fluid receiving part covers the stopper part of an adjacent impeller blade. To a top plate constituting a frame body of the apparatus, a fluid guide plate inclined inward being fixed for guiding the fluid to the impeller blades positioned under the rotating shaft of the rotor.