A centrifugal compressor comprising: a housing having a shroud-side wall surface and a hub-side wall surface, which face each other; an impeller rotationally supported in the housing; an annular diffuser passage defined in the housing by the shroud-side wall surface and the hub-side wall surface, wherein the diffuser passage has a passage cross-sectional area, and the impeller and the diffuser passage are arranged and constructed so that fluid is delivered to the diffuser passage by centrifugal action produced by rotation of the impeller; an annular movable member that is configured to be projected from one of the shroud-side wall surface and the hub-side wall surface into the diffuser passage and to be retracted from the diffuser passage, wherein the movable member has a through hole with a passage cross-sectional area smaller than the passage cross-sectional area of the diffuser passage; and an actuation mechanism (35, 37) to project and retract the movable member, wherein the other of the shroud-side wall surface and the hub-side wall surface has an abutting portion (15b; 32b) against which the movable member projected by the actuation mechanism (35, 37) abuts, and wherein the centrifugal compressor is configured and arranged so that, when the movable member abuts against the abutting portion (15b; 32b), an upstream side and a downstream side of the movable member in the diffuser passage communicate with each other via the through hole, wherein the through hole is a slit extending in a circumferential direction of the movable member, or multiple through holes which are formed so as to extend through the movable member are arranged in the circumferential direction of the movable member, wherein the holes are circular or have the shape of an oval. a housing having a shroud-side wall surface and a hub-side wall surface, which face each other; an impeller rotationally supported in the housing; an annular diffuser passage defined in the housing by the shroud-side wall surface and the hub-side wall surface, wherein the diffuser passage has a passage cross-sectional area, and the impeller and the diffuser passage are arranged and constructed so that fluid is delivered to the diffuser passage by centrifugal action produced by rotation of the impeller; an annular movable member that is configured to be projected from one of the shroud-side wall surface and the hub-side wall surface into the diffuser passage and to be retracted from the diffuser passage, wherein the movable member has a through hole with a passage cross-sectional area smaller than the passage cross-sectional area of the diffuser passage; and an actuation mechanism (35, 37) to project and retract the movable member, wherein the other of the shroud-side wall surface and the hub-side wall surface has an abutting portion (15b; 32b) against which the movable member projected by the actuation mechanism (35, 37) abuts, and wherein the centrifugal compressor is configured and arranged so that, when the movable member abuts against the abutting portion (15b; 32b), an upstream side and a downstream side of the movable member in the diffuser passage communicate with each other via the through hole, wherein the through hole is a slit extending in a circumferential direction of the movable member, or multiple through holes which are formed so as to extend through the movable member are arranged in the circumferential direction of the movable member, wherein the holes are circular or have the shape of an oval.