To provide a scroll fluid machine improved in compression efficiency by optimizing the back pressure of a movable scroll to effectively prevent the movable scroll from being overturned while securing the reliability of a scroll unit.

This scroll fluid machine 1 includes a high-pressure chamber 48 which receives high pressure generated by the discharge pressure of lubricating oil for lubricating the scroll unit 14 at the center of the rear surface 26b of the end plate 26 of the movable scroll 22 and a seal ring 52 which forms a back pressure chamber 50 reduced in pressure than the high-pressure chamber by partitioning itself and the high-pressure chamber at the outer periphery of the rear surface of end plate of the movable scroll. The seal ring includes a partly swelled section 58 at a position corresponding to the outermost peripheral side predetermined range of an outer peripheral side compression chamber 36a formed at the outer peripheral side of the lap 30 of the movable scroll in a plan view.