A centrifugal compressor comprising: an impeller including a hub and a plurality of blades (6, 6A, 6B) disposed on an outer peripheral surface of the hub at intervals in a circumferential direction; and a casing accommodating the impeller and defining an inlet passage for introducing air to the impeller along an axial direction of the impeller therein, wherein an inner peripheral surface of the inlet passage includes a narrowed portion, an inclined portion connected to a downstream side of the narrowed portion, a distance between the inclined portion and a rotational axis of the impeller in a radial direction gradually increasing from a downstream end of the narrowed portion which is an upstream end of the inclined portion toward tips of leading edges of the blades (6, 6A, 6B), and a shroud portion connected to a downstream end of the inclined portion, the shroud portion being disposed with a predetermined clearance from the tips of the blades (6, 6A, 6B), wherein the downstream end of the inclined portion is at the same position as the tips of the leading edges of the blades (6, 6A, 6B) in the axial direction of the impeller, characterized in that 0.01R1≤σ≤0.1R1 is satisfied, where R1 is a distance between a downstream end of the inclined portion and the rotational axis of the impeller in the radial direction, R2 is a distance between a downstream end of the narrowed portion and the rotational axis of the impeller in the radial direction, and σ is a constriction amount which is a difference between R1 and R2, in that a minor angle (θ) between the rotational axis of the impeller and a straight line passing through an upstream end and the downstream end of the inclined portion is 6° or less, and in that the the narrowed portion has a length of 0.5R1 or more in the axial direction of the impeller. an impeller including a hub and a plurality of blades (6, 6A, 6B) disposed on an outer peripheral surface of the hub at intervals in a circumferential direction; and a casing accommodating the impeller and defining an inlet passage for introducing air to the impeller along an axial direction of the impeller therein, wherein an inner peripheral surface of the inlet passage includes a narrowed portion, an inclined portion connected to a downstream side of the narrowed portion, a distance between the inclined portion and a rotational axis of the impeller in a radial direction gradually increasing from a downstream end of the narrowed portion which is an upstream end of the inclined portion toward tips of leading edges of the blades (6, 6A, 6B), and a shroud portion connected to a downstream end of the inclined portion, the shroud portion being disposed with a predetermined clearance from the tips of the blades (6, 6A, 6B), wherein the downstream end of the inclined portion is at the same position as the tips of the leading edges of the blades (6, 6A, 6B) in the axial direction of the impeller, characterized in that 0.01R1≤σ≤0.1R1 is satisfied, where R1 is a distance between a downstream end of the inclined portion and the rotational axis of the impeller in the radial direction, R2 is a distance between a downstream end of the narrowed portion and the rotational axis of the impeller in the radial direction, and σ is a constriction amount which is a difference between R1 and R2, in that a minor angle (θ) between the rotational axis of the impeller and a straight line passing through an upstream end and the downstream end of the inclined portion is 6° or less, and in that the the narrowed portion has a length of 0.5R1 or more in the axial direction of the impeller. in that a minor angle (θ) between the rotational axis of the impeller and a straight line passing through an upstream end and the downstream end of the inclined portion is 6° or less, and in that the the narrowed portion has a length of 0.5R1 or more in the axial direction of the impeller.