A centrifugal compressor, comprising: a casing which is configured to be horizontally split into two portions and includes an upper half portion on an upper side and a lower half portion on a lower side; an internal unit which is disposed in the casing and in which a rotor configured to rotate around an axis thereof, a bearing portion which rotatably supports the rotor, and an annular seal portion which seals a gap surrounding a circumferential surface of the rotor so as to enable the rotor to rotate are integrated; an axial movement restricting portion which includes a fitting concave portion provided in one of the casing and the internal unit and a fitting convex portion provided in the other thereof to be fitted into the fitting concave portion as a pair and restricts relative movement between the casing and the internal unit in a direction of the axis; and a tapered surface which is formed on each of the fitting concave portion and the fitting convex portion so that a width thereof in the direction of the axis increases toward an inner circumferential side in a radial direction, characterized in that in cross-sections in the radial direction of both the fitting concave portion and the fitting convex portion, the tapered surface is formed only on a side wall on a rearward side in a direction of an operational axial force applied to the internal unit and are not formed on side walls (57, 58) on the forward side, and wherein in cross-sections in the radial direction of both the fitting concave portion and the fitting convex portion, a side wall on a forward side in a direction of an operational axial force applied to the internal unit is formed perpendicular to the direction of the axis. a casing which is configured to be horizontally split into two portions and includes an upper half portion on an upper side and a lower half portion on a lower side; an internal unit which is disposed in the casing and in which a rotor configured to rotate around an axis thereof, a bearing portion which rotatably supports the rotor, and an annular seal portion which seals a gap surrounding a circumferential surface of the rotor so as to enable the rotor to rotate are integrated; an axial movement restricting portion which includes a fitting concave portion provided in one of the casing and the internal unit and a fitting convex portion provided in the other thereof to be fitted into the fitting concave portion as a pair and restricts relative movement between the casing and the internal unit in a direction of the axis; and a tapered surface which is formed on each of the fitting concave portion and the fitting convex portion so that a width thereof in the direction of the axis increases toward an inner circumferential side in a radial direction, characterized in that in cross-sections in the radial direction of both the fitting concave portion and the fitting convex portion, the tapered surface is formed only on a side wall on a rearward side in a direction of an operational axial force applied to the internal unit and are not formed on side walls (57, 58) on the forward side, and wherein in cross-sections in the radial direction of both the fitting concave portion and the fitting convex portion, a side wall on a forward side in a direction of an operational axial force applied to the internal unit is formed perpendicular to the direction of the axis.