PURPOSE: To aim at sustaining the efficiency of compression for a long period, by forming a groove in the spiral direction, for reserving therein sealing oil, in one end face of at least one of spiral plates of dynamic blade and static vane sections, and by sealing a compression space with the use of a sealing oil film formed by the oil in the groove.

CONSTITUTION: When a shaft 7 is rotated by a motor 9, a dynamic blade section 12 revolves while it is prevented from rotating. In association with the motion of the dynamic blade section, after working fluid fed from a suction pipe 15 into compression spaces 13,... is compressed, the working fluid is discharged into the outside by way of a discharge pipe. By the way, the working fluid in the spaces 13,... is completely sealed by a sealing film formed by oil reserved in grooves 20a, 22a which are formed along the spiral direction in the end faces of spiral plates 20, 22 of the dynamic blade and static vane sections 12, 14. Further the sealing film persists as far as oil exists in the grooves 20a, 22a, and therefore, the efficiency of compression may be completely prevented from lowering due to lowering of the sealing condition of sealing spaces 13. Further, the fabricating condition for the dynamic blade and static vane sections 12, 14 may be alleviated and a mass production can be realized.