A compressor includes a compression mechanism having two opposed end plates, a fixed member disposed between the two end plates, a movable member disposed between the two end plates, a bypass passage, and an opener/closer. The movable member is arranged to eccentrically move about a predetermined rotational axis to compress refrigerant in a compression chamber formed between the fixed member and the movable member. The bypass passageway has an upstream end opened to the compression chamber through which refrigerant is partially ejected from the compression chamber so as to be returned to a suction side of the compression mechanism. The cross section of the upstream end of the bypass passage is preferably elongated circumferentially about the rotational axis. The compression mechanism may include a plurality of bypass passages and a plurality of openers/closers.