To shorten an axial length of a multi-plate friction clutch device and a hydraulic power transmission including the same.

A lock-up clutch mechanism 8 included in this hydraulic power transmission 1 includes: a first friction plate 83 engaged with a clutch hub 81 fixed to a front cover 3; a second friction plate 84 engaged with a clutch drum 82 connected to an input shaft of the transmission via a damper device 10; and a lock-up piston 80 moving in an axial direction toward the front cover 3 and capable of pressing the first and second friction plates 83, 84. The clutch hub 81 includes a protrusion 81c formed so as to protrude in the axial direction toward the lock-up piston 80 and abutting against any one of the first and second friction plates 83, 84.