DISPLACEMENT MACHINE

Second arm portions 54a and 54b formed as inner peripheral cylindrical surfaces about a center axis that is an axis parallel to a rotation axis of shaft members 50a and 50b are configured to support first arm portions 44a and 44b, such that centers of sphere P1a and P1b of outer peripheral spherical portions 45a and 45b mounted to the first arm portions 44a and 44b are constrained on a center axis of the second arm portions 54a and 54b. Even when a swing piece amplitude angle (maximum swing angle) is increased by decreasing the arm length of the first arm portions 44a and 44b or when the swing piece amplitude angle (maximum swing angle) is increased with an increase in piston stroke by decreasing the diameter (bore diameter) of pistons 42a and 42b, this configuration reduces a vibration torque of vibrating the periphery, compared with a prior art positive displacement machine. This accordingly provides a lower vibration-type positive displacement machine of the small size and the high efficiency.