At a vaned diffuser or a volute casing of a centrifugal fluid machine, pressure pulsation and vibrating forces acting upon the diffuser or the volute casing are mitigated or cancelled so as to abate the noise from the centrifugal fluid machine. The fluid machine having an impeller 3 rotating about a rotating shaft 2 within a casing 1 and having a vaned diffuser 4 or volute 12 fixed to the casing 1 is constructed such that radius of the vane trailing edge of the impeller 3 and radius of the vane leading edge of the diffuser 4 or radius of the volute tongue is varied in the direction of axis of rotation and inclinations, on a meridional plane, of the vane trailing edge of the impeller 3 and the vane leading edge of the diffuser 4 or the volute tongue are set in the same orientation, thereby reduction in head and efficiency or occurrence of an axial thrust may be restrained to the extent possible to optimally abate the noise and pressure pulsation of the centrifugal fluid machine.