An apparatus for generating a rotary reciprocating motion comprises an input shaft which is driven with unidirectional rotation and an output shaft for delivering reciprocating rotary motion. A first magnetic or ferromagnetic ring is disposed about a rotation axis fixed to the input shaft and a second magnetic or ferromagnetic ring is disposed about the rotation axis fixed to the output shaft. At least one is formed as an arrangement of permanent magnets. The first and second rings are disposed one within the other around the rotation axis. The magnetic coupling between the rings in combination with the effect of an output load results in the desired reciprocating motion of the output shaft.