Disclosed is a parking lock mechanism of a power transmission apparatus which can stably supply lubrication oil to the sliding surface of a parking cam to decrease the sliding resistance of the parking cam. The parking lock mechanism 52 includes a support portion 73 for positioning a sleeve 71 with respect to an extension housing 6, and a first guide rib 74 provided on the support portion 73 for catching oil circulating in a transaxle case 4 to supply the oil to the support portion 73. The sleeve 71 has an upper portion formed with a notch 71c for allowing a parking pawl 62 to be held in abutment with a parking cam 61. The oil caught by the first guide rib 74 is supplied through the support portion 73 and the notch 71c of the sleeve 71 to the sliding surface of the parking cam 61, viz., the sliding surface between the parking pawl 62 and the parking cam 61 and the sliding surface between the parking cam 61 and the sleeve 71.