A compressor and an oil separating device therefor are provided which are capable of always maintaining a predetermined amount of oil in the compressor without additionally providing an oil separating device along a refrigerating cycle system. This results in the refrigerating cycle system having simplified piping and the refrigerant discharged from the compressor having a constant pressure, thereby preventing a function of the refrigerating cycle system from being reduced. The compressor includes a casing, a compression device having a compression chamber disposed within the casing and configured to receive, compress, and output a refrigerant, and an oil separating device disposed within the casing. The oil separating device includes a separation chamber configured to circulate the refrigerant to separate oil therefrom, a guide member configured to direct the refrigerant discharged from the compression device, and a circulation member configured to receive the refrigerant from the guide member and direct the refrigerant into the separation chamber in a direction of circulation.