PURPOSE: To allow a stable operation up to a small-flow area by making the blade exit angle on the hub side of an impeller larger than the blade exit angle on the shroud side and setting the difference between both blade exit angles to a specific range.

CONSTITUTION: The relationship between the blade exit angle β2s of the shroud side of an impeller and the blade exit angle β2h of the hub side is set to β2s<β2h, 2°=β2h-β2s≤12°. In this means, when the flow is decreased to Q/Q0=0.85 from the rated flow Q/Q0=1,0, the drift αh from the optimum value of the diffuser incidence angle on the hub side can be made within 3°. As a result, a centrifugal compressor which can perform a stable operation up to a small-flow area and has high performance in a rated flow area can be obtained. A typical example representing the relationship between the blade exit angle β2h on the hub side of the impeller and the blade exit angle β2s on the shroud side is shown by a graph, where Cm2 is the blade meridian velocity and u2 is the blade exit peripheral speed.