PURPOSE: To make an acceleration type fluid coupling higher in revolution by supporting an impeller incorporated pinion system with both an input side bearing and an output side bearing, and thereby making an impeller a closed type with the output side bearing disposed at the output side of the impeller.

CONSTITUTION: The revolution of an electric motor is transmitted to a gear accelerating device of a gear 2. A pinion 3 is driven so as to be accelerated by the gear 2. An impeller 6 acting as the driving side of a fluid coupling is incorporated in the pinion 3. The impeller incorporated pinion system is supported by both an input side bearing 4 and an output side bearing 5. The output side bearing 5 is disposed at the output side of the impeller 6 in such a way that the impeller 6 is not structurally overhanged. By this constitution, the natural frequency of the pinion system can be made high. The fluid coupling can thereby be made higher in revolution. In addition, the bearings can be made small in diameter, efficiency can thereby be enhanced concurrently.