To produce flowing water contributing to water power generation with an intermediate capacity or lower, by taking water flowing down from a mountaintop area while possessing high kinetic energy, so as to lead the water with low flow-down resistance into a waterwheel for power generation.

A headrace for water power generation takes the water from an upper section of the flowing water in a mountain dale etc., and leads the water inward as the flowing water necessary for the running of the waterwheel for the power generation, which is installed in a lower section. The headrace, which is at least partially arranged in an inclined state, leads the flowing water, taken by a sidlingly arranged section, into the waterwheel for the power generation after converting the flowing water to high-velocity flowing water from low-velocity flowing water. Additionally, the cross-sectional-direction inner periphery of the headrace is set to be decreased in inverse proportion to the flow velocity of the flowing water passing therethrough, so as to prevent the dispersion of the flowing water.