To provide a scroll fluid machine improved in volumetric efficiency by easily and surely preventing a refrigerant from leaking into the back pressure chamber of a movable scroll and reduced in machining cost.

This scroll fluid machine (1) comprises a fastening structure (62) for securing a fixed scroll (34) to a frame (18) and dividing the back pressure chamber (60) from the outside by fitting the mutually opposed fastening surfaces (34a, 18a) of the fixed scroll and the frame to each other and fastening them to each other with screws. The fastening structure is formed by inserting a seal member (64) between the fastening surfaces over the entire surfaces thereof.