An outer end of a seal element for a fixed scroll is extended to a position close to an end of an inside spiral wall of the fixed scroll, and an outwardly extended portion is formed at an outer periphery of a disc-shaped base plate of a movable scroll, so that a bottom surface of the movable scroll is always kept in a sliding contact entirely with the seal element during the orbital movement of the movable scroll. A thickness of the outwardly extended portion formed at the outer periphery of the disc-shaped base plate is made smaller than that of the disc-shaped base plate, so that the weight of the fluid machine can be smaller.