A coupling mechanism including a fluid coupling device having input and output elements, and a centrifugal type lock-up clutch for releasably engaging the input and output elements, characterized in that the lock-up clutch comprises: a cylindrical inner surface formed on the input element; a drive plate provided with friction elements displaceable in a radially outward direction for engagement with the cylindrical inner surface, and cam weights for urging the friction elements in a radially outward direction; a driven plate coupled with the output element; a damper of a resilient material provided between the drive and driven plates; and a cam surface for urging the cam weights in a radially outward direction according to the degree of relative displacement between the drive and driven plates.