To provide a lubricating structure of a spline fitting part in which lubricating fluid for a spline fitting part is not drained to a space opened to the atmosphere.

A rotor shaft 13 having an oil path 22 and a male spline 21 is supported in a case 9, and a flange part 6b of a flywheel 6 is supported in a damper housing 14 opened to the atmosphere. A flange part 6b in a bottomed cylinder shape has a female spline 24 formed on its inner peripheral surface and runs through a barrier 15 for separating the space in the case 9 and the space in the damper housing 14. The lubricating oil supplied from the oil path 22 passes through the spline fitting part 20, which is formed by fitting the male spline 21 and the female spline 24, and drained from an opening end 26 of the flange part 6b to a case 3.