Hyrdraulic motor

The invention relates to a hydraulic motor having an outer casing and eccentric means for rotating a power shaft by means of fluid through a pressure chamber arrangement. The eccentric means comprise an eccentric part formed in the power shaft, a first eccentric ring between the outer casing and an inner casing, and a second eccentric ring mounted with bearings around the eccentric part and connected fixedly and concentrically to the first eccentric ring, whereby the pressure chamber arrangement is located between the first eccentric ring and the inner casing so that the first eccentric ring drives the power shaft through the second eccentric ring, and the eccentric rings form a substantially non-rotating entity that only performs an eccentric movement and by means of this eccentric movement rotates the power shaft.