A hermetic rotary compressor includes a sealed case, an electrically-driven mechanism installed in the sealed case and a compressing mechanism for compressing the sucked-in refrigerant. The compressing mechanism has a cylinder defining a compression chamber into which an eccentric roller of the electrically-driven mechanism is accommodated. Upper and lower flanges are respectively fixed to upper and lower portions of the cylinder so as to support the rotary shaft and seal the compression chamber. At least one resonance chamber is formed at an inner peripheral surface of a discharge port formed in the upper flange, whereby the resonance chamber communicates with the discharge port. A closure member is provided for opening/closing the resonance chamber. The closure member is biased closed by a spring disposed in a hole formed at the inner peripheral surface of the discharge port of the upper flange, the hole and resonance chamber having a common entrance. The resonance chamber is opened during a compression operation and is closed when the refrigerant is discharged by the closure member.