A centrifugal compressor comprising: an impeller; a casing configured to rotatably house the impeller allowing rotation about a rotational axis; a gas channel, at least provided in the casing, configured to circulate gas passing through the impeller; a treatment hollow part provided inside the casing; a first channel, open to the gas channel at a vicinity of and on the downstream side of a blade leading edge of the impeller, configured to introduce gas into the treatment hollow part from the gas channel; a second channel, open to the gas channel at a position on the upstream side of the blade leading edge, configured to discharge gas inside the treatment hollow part into the gas channel, and configured to impart a swirl component in an opposite rotational direction of the impeller to gas discharged via the second channel, wherein either the first channel and the second channel are formed in slit shapes extending in the entire circumferential direction and the second channel is provided with guide vanes or the first channel and the second channel are formed from multiple holes provided at equal intervals in the entire circumferential direction; a constricting part, provided at a position on the upstream side of an opening part of the second channel, configured to constrict the gas channel to a gas channel diameter at a position of the opening part of the second channel; and a rectifying part, provided in the constricting part, and including at least one rectifying element configured to rectify gas supplied to the constricting part in a direction that minimizes a swirl component about the rotational axis and also increases a component in a direction of the rotational axis. an impeller; a casing configured to rotatably house the impeller allowing rotation about a rotational axis; a gas channel, at least provided in the casing, configured to circulate gas passing through the impeller; a treatment hollow part provided inside the casing; a first channel, open to the gas channel at a vicinity of and on the downstream side of a blade leading edge of the impeller, configured to introduce gas into the treatment hollow part from the gas channel; a second channel, open to the gas channel at a position on the upstream side of the blade leading edge, configured to discharge gas inside the treatment hollow part into the gas channel, and configured to impart a swirl component in an opposite rotational direction of the impeller to gas discharged via the second channel, wherein either the first channel and the second channel are formed in slit shapes extending in the entire circumferential direction and the second channel is provided with guide vanes or the first channel and the second channel are formed from multiple holes provided at equal intervals in the entire circumferential direction; a constricting part, provided at a position on the upstream side of an opening part of the second channel, configured to constrict the gas channel to a gas channel diameter at a position of the opening part of the second channel; and a rectifying part, provided in the constricting part, and including at least one rectifying element configured to rectify gas supplied to the constricting part in a direction that minimizes a swirl component about the rotational axis and also increases a component in a direction of the rotational axis.