PURPOSE: To obtain a change gear having simple structure and torque limiter function by selecting combination of opposing magnetized parts thereby changing the rotational ratio between rotary shafts.

CONSTITUTION: Upon rotation of a first rotary shaft 1 on the input side through a driving means 2, a magnetized part 6A of a first rotary body 6 rotates to cause attraction between poles at the opposing magnetized parts 22 resulting in rotation of an amount corresponding to the number of moving poles of the first rotary body 6. A rotational ratio switching mechanism 12 is then switched to move a moving arm 10 and when the first rotary body 6 opposes to a magnetized part 20 having different number of poles, the rotational speed varies. Since the magnetized parts 20, 22, 24 having different number of poles can have an identical outer diameter through setting of pole pitch and since the rotary bodies 6, 19 are kept from contact at all times, rotational ratio can be modified by simply moving the rotary body 6 in the axial direction resulting in simplication of mechanism. Furthermore, when the rotational resistance of the second rotary body 19 exceeds the magnetic coupling force between the magnetized parts, the first rotary body idles to function as a torque limiter.