A balancing device (100) for a rotary apparatus including a rotary body which is configured to pivot or swivel about at least one rotary shaft (6a) is provided. The balancing device (100) includes a magnet assembly and a torque adjusting mechanism. The magnet assembly includes a combination of two or more magnets (11, 12), and the torque adjusting mechanism is configured to adjust a torque generated by the combination of the two or more magnets (11, 12). The balancing device (100) generates an output torque in the form of a cosine curve or sine curve which optimally matches with an unbalancing torque of the rotary body. The balancing device (100) has a small size and is invulnerability to fatigue failure.
