A cam ring is capable of moving while rolling on a cam support surface. The cam ring is provided such that within a range in which the cam ring can move on the cam support surface, an eccentricity amount increasing-side angle is always greater than an eccentricity amount decreasing-side angle. On a plane perpendicular to the rotation axis of a driving shaft, the eccentricity amount increasing-side angle is an angle, in a direction opposite to a rotation direction of the driving shaft, from a first reference line, which connects a tangent point between the cam ring and the cam support surface to a rolling center of the cam ring, to a starting end of a first discharge port. The eccentricity amount decreasing-side angle is an angle, in the rotation direction of the drive shaft, from the first reference line to a terminal end of the first discharge port.