PURPOSE: To reduce a sliding force and eliminate a maintenance for a long period of time by a method wherein a compressing means is provided at one side of a movable scroll and an expansion means is provided at the other side of the movable scroll.

CONSTITUTION: In case of a compressing means 21, a first movable lap 52 is rotated in a clockwise direction under a primary rotation of a movable scroll 5, a compressing chamber 23 is formed from outer peripheral ends of both laps 32 and 52. The compressing chamber 23 is shrinked while moving in a scroll form toward a central part and this is communicated with a discharging port 26 from inner peripheral ends of both laps 32 and 52. In turn, simultaneously, in case of an expansion means 22, the first movable lap 53 is rotated in a counter- clockwise direction, an expansion chamber 24 is formed at the inner peripheral ends of both laps 42 and 53, the expansion chamber 24 expands while mixing in a scroll form toward outside and this is communicated with a discharging port 28 from an outer peripheral ends of both laps 42 and 53. A compressing means 21 is formed at one side of the movable scroll 5 and the expansion means 22 is formed at the other side, so that a thrusting force of the movable scroll 5 is balanced and the pressing forces of each of the laps 32, 42, 52 and 53 against the bate plates 31, 41 and 51 can be reduced and a sliding force of each of the laps 32, 42... is reduced and a wear at the extreme end can be reduced.