A hydraulic power generating apparatus which can be easily disposed in a water channel, such as a waterway or a water conducting pipe. The hydraulic power generating apparatus comprises a horizontal rotor supporting housing (4) having a rotor, a holding body (5) erected on an upper surface of the rotor supporting housing (4), a support ring (2) in which the rotor supporting housing (4) is fixed, and a power generator (11). The rotor supporting housing (4) is integrally fixed within the support ring (2) by the holding body (5). The power generator (11) is disposed on the upper part of the holding body (5) protruding from the support ring (2), and the support ring (2) is formed with attachment portions (2A, 2B) for fixing the rotor supporting housing (4) in a water channel.