Disclosed herein is an aerogenerator having a horizontal maintaining means. The aerogenerator of the present invention includes a support pillar which is placed upright on the ground and has a hollow space therein. The aerogenerator further includes a rotational support unit which is provided on the upper end of the support pillar so as to be rotatable. The rotational support unit includes a rotational body and a rotational support base which supports the lower end of the rotational body. The opposite ends of the rotational support base extend predetermined lengths from the rotational body outwards. The aerogenerator further includes vane units which include a main vane and a subsidiary vane provided on the respective opposite ends of the rotational support base of the rotational support unit. The main vane and the subsidiary vane have different weights. The aerogenerator further includes a generating unit which converts the rotating force of the vane units into electric energy, a rotating force transmission unit which transmits the rotating force of the vane units to the generating unit, and the horizontal maintaining means which connects the vane units to the rotational body to maintain central axes of rotating shafts of the vane units horizontal.