To provide a power transmission device enhancing mountability.

The power transmission device includes a converter housing 20 connected to an engine output shaft 10; a turbine hub 34 connected to a transmission input shaft 11; and a wet-type lock-up clutch mechanism 50 for changing engagement and disengagement states of the converter housing 20 and the turbine hub 34. The device also includes a working oil passage 11a and a sealing member 28. The working oil passage is formed into a shape to contact with the transmission input shaft 11, and supplies oil for moving a piston 56 of the lock-up clutch mechanism 50 to a working oil chamber 25. The sealing member is installed to contact with the transmission input shaft 11, and seals the oil leakage from the working oil passage 11a to the mounting portion of the turbine hub 34. The mounting portion of the turbine hub 34 and the contact portion of the sealing member 28 in the transmission input shaft 11 are respectively set at positions aligned on a straight line orthogonal to an axis L1 of the transmission input shaft 11.