A lockup clutch mechanism of a hydraulic transmission device includes a lockup piston that is capable of moving toward a front cover to press first and second friction plates, and a flange member that together with the lockup piston defines an engagement-side oil chamber. The front cover and the lockup piston define a first lubricant passage that supplies hydraulic oil to the first and second friction plates. A second lubricant passage communicating with the first lubricant passage is formed in a centerpiece of the front cover. A first shaft oil passage communicating with the engagement-side oil chamber and a second shaft oil passage communicating with the second lubricant passage are formed in an input shaft.