A compact hydropower generator adopting multiple rotary drums comprises a water reservoir for changing the flow direction of water that flows along a river and for temporarily storing the water. A base body is located at a lower side of the water reservoir and has a drainage way formed at an end of a downwardly inclined portion thereof. An upper closing member and a lower closing member are provided at opposite sides of an upper end of the base body. The upper closing member is configured to communicate with the water reservoir, and the lower closing member is configured to communicate with the drainage way through a plurality of drain pipes. A power generating unit is located between the upper and lower closing member. When the water stored in the water reservoir is introduced thereinto through a plurality of water supply pipes, the power generating device rotates about a plurality of shafts due to the potential energy of the water to obtain power. An accelerator and a generator are coupled to the lower ends of the shafts.
