A windmill-type electric generation system including four rotary blade units (10, 12, 14, 16) mounted on opposite ends of corresponding rotary shafts in pairs, a first power transmission mechanism for transmitting the rotating movement of the blade units (12, 14) to an armature (110) of an electric generator (100), a second power transmission mechanism for transmitting the rotating movement of the blade units (10, 16) to a magnetic pole (120) of the electric generator (100), and the electric generator (100) for generating electricity through the rotation of the armature (110) and the magnetic pole (120) in the opposite directions, which is accomplished by the rotating movement of the blade units (10, 12, 14, 16) transmitted to the armature (110) and the magnetic pole (120) by the power transmission mechanisms.