a driving shaft that is rotatable clockwise and counterclockwise directions, and that has an eccentric portion of a predetermined size;

a cylinder having a predetermined inner volume;

a roller rotatably installed on an outer circumferential surface of the eccentric portion so as to contact an inner circumferential surface of the cylinder, wherein the roller performs a rolling motion along the inner circumferential surface of the cylinder and forms a fluid chamber therewith in which fluid is compressed;

a vane elastically installed in the cylinder so as to contact the roller;

upper and lower bearings respectively installed at upper and lower portions of the cylinder, the upper and lower bearings rotatably supporting the driving shaft and hermetically sealing the inner volume of the cylinder;

a plurality of suction ports and a plurality of discharge ports that each communicate with the fluid chamber so as to suction and discharge fluid;

a suction plenum that communicates with at least one of the plurality of suction ports, and that stores fluid therein; and

a compression mechanism configured to form compressive spaces of different sizes in the fluid chamber based on a rotational direction of the driving shaft, wherein the compression mechanism provides a first compression capacity in a clockwise rotational direction and a second compression capacity in a counterclockwise rotational direction.