A horizontal type compressor comprising: a differential pressure plate for dividing an inside of a casing into a high pressure chamber and a lower pressure chamber and thus maintaining an oil level of the high pressure chamber to be higher than that of the lower pressure chamber; and a lubricating unit for supplying oil stored in the high pressure chamber to each sliding part in the compressor and making the oil which finished a lubricating operation return to the high pressure chamber from the lower pressure chamber. The compressor smoothly supplies refrigerant oil and minimizes an amount of the refrigerant oil discharged outside the compressor, thereby prolonging a life of the compressor and increasing a reliability of the compressor. Also, the differential pressure plate and the muffler are integrally formed, thereby reducing a fabricating cost and reducing an assembling process.