A compressor having a rotary compression mechanism including in a housing the rotary compression mechanism for compressing gas, and a driving unit for driving the rotary compression mechanism, the rotary compression mechanism comprising: a cylinder having a cylindrical inner surface; a crankshaft extending through the cylinder, being rotationally driven around a central axis of the cylinder by the driving unit, and having an eccentric axial portion eccentric to the central axis of the cylinder; plate members (43, 61) for covering apertures at both end portions of the cylinder; a discharge port (45, 65) formed in at least one of the plate members, and communicating with an inside of the cylinder; a boss (46, 62) in a cylindrical shape integrally disposed with the plate member in which the discharge port is formed, and rotatably supporting the crankshaft that extends through the boss; a muffler cover whose outer periphery abuts against the plate member, and whose inner periphery opposes an outer peripheral surface of the boss so as to form a muffler chamber into which refrigerant is fed from the cylinder through the discharge port; a refrigerant outlet formed between the inner periphery of the muffler cover and the outer peripheral surface of the boss, the refrigerant outlet feeding the refrigerant from the muffler chamber into the housing; characterized in that the rotary compression mechanism further comprises a collecting member disposed at the refrigerant outlet so as to collect lubricant oil contained in the refrigerant, a peripheral groove is formed in the boss such that the peripheral groove continuously extends in a peripheral direction of the boss at a position opposing the inner periphery of the muffler cover, and the collecting member is placed in the peripheral groove, and is disposed between the inner periphery of the muffler cover and the outer peripheral surface of the boss. a cylinder having a cylindrical inner surface; a crankshaft extending through the cylinder, being rotationally driven around a central axis of the cylinder by the driving unit, and having an eccentric axial portion eccentric to the central axis of the cylinder; plate members (43, 61) for covering apertures at both end portions of the cylinder; a discharge port (45, 65) formed in at least one of the plate members, and communicating with an inside of the cylinder; a boss (46, 62) in a cylindrical shape integrally disposed with the plate member in which the discharge port is formed, and rotatably supporting the crankshaft that extends through the boss; a muffler cover whose outer periphery abuts against the plate member, and whose inner periphery opposes an outer peripheral surface of the boss so as to form a muffler chamber into which refrigerant is fed from the cylinder through the discharge port; a refrigerant outlet formed between the inner periphery of the muffler cover and the outer peripheral surface of the boss, the refrigerant outlet feeding the refrigerant from the muffler chamber into the housing; characterized in that the rotary compression mechanism further comprises a collecting member disposed at the refrigerant outlet so as to collect lubricant oil contained in the refrigerant, a peripheral groove is formed in the boss such that the peripheral groove continuously extends in a peripheral direction of the boss at a position opposing the inner periphery of the muffler cover, and the collecting member is placed in the peripheral groove, and is disposed between the inner periphery of the muffler cover and the outer peripheral surface of the boss.