To effectively cool a magnetic coupling without increasing a space of providing the magnetic coupling even when application is made to a magnetic coupling which transmits the rotation of a power turbine to a reduction gear in an exhaust heat collection power generation device constituting an exhaust heat collection type marine propulsion device which is installed for collecting exhaust heat of a diesel engine (internal combustion engine), for example, as the propulsion main engine of a ship.

A plurality of through holes 74 which penetrate an inner rotor 61 in the thickness direction and through each of which a cooling medium passes, are formed in an inner rotor 61 in which magnets 72 forming an N-pole and magnets 73 forming an S-pole are alternately arrayed along the circumferential direction in the circumferential edge part of a disk-like inner yoke 71 having the predetermined thickness and which is fixed to a first rotary shaft 13a to be a drive side and is rotated together with the first rotary shaft 13a.