To solve the problem of a small-sized scroll fluid machine wherein since the diameter of a swivel bearing is small, a slide bush mechanism cannot be applied, a clearance gap between lap side walls is enlarged to increase an internal leakage and largely lower the efficiency, and the radius of revolution of a swivel shaft is fixed not to improve the efficiency in a driving shaft separation structure in which a driving shaft, the main shaft of which is integrated with the swivel shaft and a motor shaft are separated.

In this shaft structure of a scroll fluid machine, the driving shaft 7, in which the swivel shaft 1 inserted in a swivel bearing and the main shaft supported by a rolling bearing at one portion are integrated with each other, and the motor shaft 8 formed by one cylinder are separated from each other. The motor shaft is inserted with an interfit clearance in a fitting hole formed concentrically in a cylinder of the main shaft part on one side of the driving shaft and having a length several times as large as the diameter to a fixed length, whirl-stopped and connected. The driving shaft is provided with two weights, and a spring 13 is mounted between the motor shaft and the driving shaft so that the force in the direction of enlarging the turning radius is applied by the inclination in the interfit clearance of the driving shaft.