A compressor is provided. The compressor includes a housing, a valve plate, a cylinder block, piston units, a cam element, a driving shaft and a motor. The valve plate is fixed to one end of the housing. The cylinder block is rotatable relative to the valve plate and has cylinder bores disposed in a circumferential direction. A portion of the cylinder block is received in the valve plate. The piston units are disposed the cylinder bores. The cam element is fixed to the housing and is in contact with one end of the piston unit. The cam element has an inclined cam surface. One end of the driving shaft is coupled to the cylinder block. The motor is fixed to an opposite end of the housing, while a rotating shaft is coupled to an opposite end of the driving shaft.