A mechanism for mechanically coupling a driving source and a driven member. The mechanism includes a first member coupled to the driving source and a second member coupled to the driven member. A resilient member exerts a force to bring the first and second members into pressure contact at a contact surface. A vibration is excited in the contact surface of the first member to produce a levitation force, based on an ultrasonic levitation, acting upon the second member. Frictional force between the first member and the second member is changed depending on the levitation force, thereby changing power transmitted between the first member and the second member.