A centrifugal compressor having a casing that houses an impeller allowing rotation about a rotational axis C, a gas channel, a treatment hollow part provided inside the casing, a first channel open to the gas channel on the downstream side of the blade leading edge of the impeller, a second channel open to the gas channel at the upstream side of the blade leading edge, a guide vane that imparts a swirl component in an opposite rotational direction of the impeller to gas discharged from the second channel, a constricting part that constricts the gas channel, and a rectifying part that rectifies gas in a direction that minimizes the swirl component about the rotational axis C and also increases the component in the direction of the rotational axis C.