An apparatus includes a blade unit including having upright blades connected fixedly to an upright rod that has a lower end disposed pivotally in a base such that the blade unit is rotatable relative to the base to convert wind energy into a mechanical rotary power output, and coupled to a generator in the base to convert the mechanical rotary power output into electric power. Each blade has opposite first and second side surfaces. The first side surface of each blade faces the second side surface of an adjacent blade. A wind-collecting unit includes upright plates fixed on the base, angularly equidistant and disposed around the blade unit. Any two adjacent plates define an inwardly converging wind-guiding channel therebetween. The plates are shaped so that wind is guided by the plates to blow onto the first side surfaces of the blades via the wind-guiding channels.