| The objectives of this study was to improve construction cost, upstream migration efficiency, maintenance work when constructing and operating the fishway, because fishways were still needed for the fish to migrate upstream in various rivers (mainly, small and medium-sized). Although the construction of fishway has been ongoing for approximately 6 decades in Japan, there is room for further improvement in design of fishway. Therefore, we proposed to dig existing concrete structures like in-river barriers (e.g., headworks, weirs, or dams) to improve the above subjects. We considered for the shape of the slit and the safety of the structure, and constructed slit-type fishway in the Tatsunokuchi-valley in Sendai city. As a result, because to the slit-type fishway that was set up, the water head required for upstream migration of fish was secured at a low cost.