PURPOSE: To prevent the breakage of laps and lower vibration and noise by removing a lap gap in a low speed zone while providing a lap gap in a high speed zone.

CONSTITUTION: When a rotating speed is low with a high gas compression force, a gas force rotation moment is higher than an inertial rotation moment and a driving element 7 is rotated around a shaft body bringing the lap side walls of a revolving scroll 3 and a fixed scroll 2 into contact with each other to remove a gap. On the contrary, when the rotating speed is high with a low gas compression force, the inertial rotation moment is higher than the gas force rotation moment and the driving element 7 is rotated in the opposite direction to above separating the lap side walls of the revolving scroll 3 and the fixed scroll 2 from each other to increase the gap.