<p>A power transmitter for transmitting a driving force from a vehicle-mounted drive source to a vehicle-mounted rotating apparatus comprises a driving side rotating body coupled mechanically with the vehicle-mounted drive source, and a driven side rotating body arranged coaxially with the driving side rotating body and coupled mechanically with the drive shaft of the vehicle-mounted rotating apparatus. The power transmitter is further provided with a magnetic coupling arranged in at least one of the driving side rotating body and the driven side rotating body and transmitting a rotary driving force from the driving side rotating body to the driven side rotating body by magnetic force under such a state as a predetermined clearance is maintained between the driving side rotating body and the driven side rotating body. Consequently, the power transmitter can make the natural frequency sufficiently lower than the frequency of vibration generated from the vehicle-mounted rotating apparatus at the time of idling of vehicle.</p>
