A friction engaging device capable of obtaining a large transfer torque capacity with a compact and simple construction and smoothly connecting and disconnecting friction engaged members. A wet type multi-disc clutch has a clutch case, a hub and a main clutch. A variable length joint is provided between an inner cylindrical portion of the clutch case and a cylindrical portion of the hub. The variable length joint is constructed mainly of a first cam plate so held as to be slidable in the axial direction on the hub, a second cam plate so held as to be rotatable relatively to the clutch case, and a plurality of rollers interposed between the first and second cam plates. A tube type clutch for making the second cam plate and the clutch case frictionally engage with each other, is provided in a gap between the second cam plate and the inner cylindrical portion of the clutch case.