A compressor in which an electric motor and a compressing mechanism are accommodated in a case, a main shaft and an auxiliary shaft of a rotating shaft of the motor are supported by a radial plain bearing and a rolling bearing with a predetermined clearance given to the rotating shaft in an axial direction, a flange portion that contacts with a main-shaft receiving member of the radial plain bearing to align the rotating shaft with the compressing mechanism is provided on the main shaft, and preload toward the side of the rolling bearing is given to the rotating shaft. In this constitution, a prevention member for preventing contact and/or collision of the rotating shaft with the main-shaft receiving member is provided between opposing faces of the flange portion and the main-shaft receiving member.