To provide a scroll fluid machine that can improve reliability in abrasion resistance of a power transmission mechanism including a pin member and a ring member. The machine includes a driving scroll member (20), a driven scroll member (22), and a power transmission mechanism (26) that transmits power to synchronously rotate both scroll members (20, 22) and allow the scroll members to revolve and orbit relative to each other. The power transmission mechanism (26) includes a pin (30) attached to the driven scroll member (22), a ring body (34) provided in the driving scroll member (20) and having an inner circumference in contact with an outer circumference of the pin (30), and a circular groove (32) housing the ring body (34) and having an inner circumference in contact with an outer circumference of the ring body (34). Of surface contact pressure in a contact portion between the outer circumference of the pin (30) and the inner circumference of the ring body (34), and surface contact pressure in a contact portion between the outer circumference of the ring body (34) and the inner circumference of the circular groove (32), the contact portion having higher surface contact pressure has a larger frictional torque.