PURPOSE:To generate a kinetic output with applied pressure as main input by applying constant pressure to an eccentric shaft rotor, and generating a differential thrust having the eccentric shaft as a supporting point. CONSTITUTION:A rotor 6 having an eccentric shaft 5 extended through and fixed to it is housed in a stator 11 as a fluid cylinder, the pressured surface of the rotor 6 is subjected to constant pressure and a differential thrust is generated by the difference in pressure receiving area having the eccentric shaft 5 as the supporting point. On the other hand, an output shaft 1 is held by the stator 11 through a bearing 18, and its inner surface gear 2 is geared with an eccentric shaft gear 4 in the gearing point 3. The eccentric shaft 5 is extended through both side plates 7, 8 so that they are simultaneously rotatable. When a fluid is introduced through a normal rotation pressure applying hole 9 for pressurization, half of the stator chamber partitioned by the rotor 6 is subjected to constant pressure. When a load is added to the output shaft 1 at this time, the eccentric shaft 5 works as the supporting point to cause a differential thrust by the dimensional difference between pressure receiving areas 14, 15 of positive and reverse thrusts, and the rotor 6 is rotated to rotationally drive the output shaft 1 through the eccentric shaft 5.