A centrifugal fluid machine is provided with: a rotor; a low-pressure compression section which is provided on one axial side of the rotor; a high-pressure compression section which is provided on the other axial side of the rotor; a partition wall (13) which separates the low-pressure compression section and the high-pressure compression section; and a high-pressure-side discharge flow passage (54) which is formed on the high-pressure compression section side of the partition wall (13), extends in the radial direction of the rotor, and is provided along the partition wall (13). The partition wall (13) has: a wall body (71); a flow passage modification-suppressing member (72) which is provided between the wall body (71) and the high-pressure-side discharge flow passage (54) and which can modify the high-pressure-side discharge flow passage (54); and a pressing mechanism (73) which is provided between the wall body (71) and the flow passage modification-suppressing member (72) and which can press the flow passage modification-suppressing member (72) toward the high-pressure-side discharge flow passage (54).