To prevent an operating state of a rotor shaft of a power turbine from showing power swing and entering into an overspeed state when this invention is applied to a magnetic coupling for use in transmitting a rotation of the power turbine to a reduction gear in an exhaust heat recovery power generator device constituting an exhaust heat recovery type ship propulsion device installed as a unit for exhaust heat recovery for Diesel engine (internal combustion engine) acting as a main propulsion machine for a ship, for example.

There is provided a twisting angle measuring device 201 for always measuring a relative twisting angle between a first rotating shaft 13a and a second rotating shaft 24a.