Abstract: Provided are a rotary device for fluid power generation and a fluid power generation device that are capable of converting the kinetic energy of a fluid to an electric energy. By utilizing a longitudinal vortex as a driving force, a rotary body such as a cylinder as a high-strength and tough wing-shaped member can be rotated, and power can be efficiently generated in a wide range of flow rate without letting the longitudinal vortex disappear even if the flow rate changes in a wide range. This rotary device for power generation includes a rotary body 3; and a wake body 8 that is a distance away from the rotary body 3 toward the downstream side of a flow direction 10 of the fluid, and has at least one crossover section at which the wake body 8 intersects with the rotary body 3.