In this paper, a hydroelectric power generator that can extract the water flow energy from the hydroelastic response of an elastically supported rectangular wing is experimentally investigated. An electric motor is used to excite pitching oscillations of the wing. The wing and the electric motor are supported by leaf springs that are designed to function both as a linear guide for the sway oscillations and as elastic elements. The wing mass in the sway direction necessary to achieve a hydroelastic response is obtained by utilizing a mechanical snubber mechanism. The load to generate electricity is provided equivalently by magnetic dampers. In a previous paper(1), the power generation rate and the efficiency of a single-wing model were examined through experiments, and the feasibility of a flapping wing hydroelectric power generator was verified. In this paper, the influence of neighboring wings is examined by using two experimental apparatuses with the intention of achieving a practical cascade-wing generator. Tests showed that a cascade moving in-phase with neighboring wings with smaller gaps between the wings has a higher rate of electric power generation.