words the output gear 16 is connected to the fluid coupling 21 via the planetary gear mechanism 19 including the planetary gears 17a and 17b so that the rotation of the power turbine 12 is transmitted to an output pump wheel 21c of the fluid coupling 21 the epicyclic gear 19 is employed because it has a large moderating ratio and a high transmission efficiency to the output pump 21c there is fixedly provided a gear 20 which rotates with the pump 21c and to the crankshaft 15 there is fixedly provided a crankshaft gear 23 another epicyclic gear 40 for connecting the crankshaft 23 with the gear and for rotating the power turbine 12 in both normal and reverse senses will now be explained the epicyclic gearing 40 comprises a sun gear shaft 42 a sun gear 41 a ring gear 44 engaged with plural planetary gears 43 at intervals in the circumferential direction thereof and surrounding circumferentially the sun gear 41 and a carrier 45 for maintaining the relative relationship of position between the planetary gear 43 and the sun gear 41 at constant while rotating the planetary gear 43 around the sun gear 41 autorotationally as well as revolutionally the sun gear shaft 42 is provided with a first transmission gear 46 engaged.