To provide a hydraulic transmission device capable of reducing a diameter of a clutch member while securing a necessary area of a friction engagement surface.

This hydraulic transmission device includes a hydraulic transmission means 20 transmitting drive force of a drive source transmitted to an input member 10 to an output shaft 50 via working fluid, a lock up clutch 30 including an input side clutch member C1 and an output side clutch member C2 and transmitting drive force transmitted to an input member directly to the output shaft, and a damper means 40 connecting the input member and the lock up clutch via elastic bodies 44a, 44b. At least one of the clutch members at an input side and an output side includes main bodies 32, 34, and friction engagement members 37, 36 provided rotatably as one unit with the main bodies. The body has an annular shape and includes a curved surface part 32c, 34b separating from another clutch member as it goes to radial direction outside at a radial direction outside end part. An installation area of the friction engagement member overlaps an installation area of a curved surface part in a radial direction.